https://shio-chan-dev.github.io/jeanblog/categories/leetcode/Recent content in LeetCode on Jeanphilo BlogHugo -- 0.159.2en-usFri, 03 Apr 2026 17:54:22 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/backtracking/46-permutations/Fri, 03 Apr 2026 17:54:22 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/backtracking/46-permutations/A practical guide to LeetCode 46 covering used[] state tracking, leaf-only collection, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/backtracking/78-subsets/Thu, 02 Apr 2026 13:48:57 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/backtracking/78-subsets/A practical guide to LeetCode 78 covering subset backtracking, the startIndex invariant, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/133-clone-graph/Thu, 19 Mar 2026 13:18:26 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/133-clone-graph/Clone a connected undirected graph by mapping original nodes to cloned nodes, with DFS and BFS variants, cycle handling, correctness reasoning, and runnable implementations in six languages.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/binary-search/2089-find-target-indices-after-sorting-array/Wed, 18 Mar 2026 13:49:55 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/binary-search/2089-find-target-indices-after-sorting-array/Sort the array, locate the target block with lower and upper bounds, and return every target index, with tradeoff analysis, engineering mappings, and runnable implementations in six languages.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/binary-search/2529-maximum-count-of-positive-integer-and-negative-integer/Wed, 18 Mar 2026 13:49:55 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/binary-search/2529-maximum-count-of-positive-integer-and-negative-integer/Count negatives and positives in a sorted array by locating the boundaries around zero with lower-bound and upper-bound binary search, with engineering mappings and runnable implementations in six languages.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/binary-search/34-find-first-and-last-position-of-element-in-sorted-array/Wed, 18 Mar 2026 13:49:55 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/binary-search/34-find-first-and-last-position-of-element-in-sorted-array/Find the start and end positions of a target in a sorted array by combining lower-bound and upper-bound binary search, with boundary reasoning, engineering mappings, and runnable implementations in six languages.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/binary-search/35-search-insert-position/Wed, 18 Mar 2026 13:49:55 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/binary-search/35-search-insert-position/Find the insertion index of a target in a sorted array with lower-bound binary search in O(log n), with boundary reasoning, engineering mappings, and runnable implementations in six languages.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/binary-search/744-find-smallest-letter-greater-than-target/Wed, 18 Mar 2026 13:49:55 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/binary-search/744-find-smallest-letter-greater-than-target/Find the smallest character strictly greater than a target in a sorted circular array by using upper-bound binary search and wrap-around logic, with pitfalls, engineering mappings, and runnable implementations in six languages.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/102-binary-tree-level-order-traversal/Mon, 16 Mar 2026 13:00:56 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/102-binary-tree-level-order-traversal/A practical guide to LeetCode 102 covering level-by-level BFS, level-size boundaries, DFS depth buckets, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/101-symmetric-tree/Mon, 16 Mar 2026 13:00:55 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/101-symmetric-tree/A practical guide to LeetCode 101 covering mirror recursion, pairwise BFS checks, symmetry contracts, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/100-same-tree/Mon, 16 Mar 2026 13:00:54 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/100-same-tree/A practical guide to LeetCode 100 covering synchronous recursion, pairwise BFS validation, structural equivalence, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/226-invert-binary-tree/Fri, 06 Mar 2026 17:58:23 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/226-invert-binary-tree/A practical guide to LeetCode 226 covering tree mirroring, recursive left-right swaps, BFS traversal, and engineering mappings.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/104-maximum-depth-of-binary-tree/Fri, 06 Mar 2026 17:58:22 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/104-maximum-depth-of-binary-tree/A practical guide to LeetCode 104 covering the depth definition, recursive DFS, level-order BFS, engineering mappings, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/94-binary-tree-inorder-traversal/Fri, 06 Mar 2026 17:58:21 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/binary-tree/94-binary-tree-inorder-traversal/A practical guide to LeetCode 94 covering left-root-right traversal, recursion, explicit stacks, engineering mappings, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/146-lru-cache/Thu, 12 Feb 2026 13:51:08 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/146-lru-cache/Implement LRUCache with O(1) average get/put by combining a hash map for lookup and a doubly linked list for recency order. Includes ACERS reasoning, engineering mapping, and runnable multi-language code.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/19-remove-nth-node-from-end-of-list/Thu, 12 Feb 2026 13:50:28 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/19-remove-nth-node-from-end-of-list/From naive two-pass traversal to one-pass fast/slow pointers, this ACERS guide explains Remove Nth Node From End of List with correctness intuition, edge cases, engineering mappings, and runnable multi-language code.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/linked-list/138-copy-list-with-random-pointer/Wed, 11 Feb 2026 07:59:32 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/linked-list/138-copy-list-with-random-pointer/The core of copying a random-pointer list is mapping original node identity to copied node identity, then rebuilding next/random pointers. This article uses the ACERS structure to cover intuition, engineering analogies, pitfalls, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/2-add-two-numbers/Wed, 11 Feb 2026 07:54:26 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/2-add-two-numbers/Add two non-negative integers represented by reverse-order linked lists. This ACERS-style guide explains digit-by-digit carry propagation with engineering mappings and runnable multi-language code.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/148-sort-list/Tue, 10 Feb 2026 17:07:38 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/148-sort-list/Sort a singly linked list in O(n log n) time using split + recursive merge sort. This guide explains derivation, invariants, engineering mappings, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/23-merge-k-sorted-lists/Tue, 10 Feb 2026 17:05:53 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/23-merge-k-sorted-lists/Upgrade from LeetCode 21 to k-way merge: derive why sequential merge degrades, then use divide-and-conquer to reach O(N log k), with heap comparison and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/142-linked-list-cycle-ii/Tue, 10 Feb 2026 10:47:56 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/142-linked-list-cycle-ii/Return the first node where a singly linked list enters a cycle without modifying the list: use Floyd fast/slow pointers to detect a meeting point, then reset one pointer to head and move both one step to localize the entry in O(n) time and O(1) space.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/21-merge-two-sorted-lists/Tue, 10 Feb 2026 10:47:02 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/21-merge-two-sorted-lists/Merge two sorted linked lists in O(m+n) with sentinel node and two pointers, with iterative and recursive comparison, engineering mapping, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/41-first-missing-positive/Tue, 10 Feb 2026 10:25:53 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/41-first-missing-positive/Find the first missing positive in O(n) time and O(1) extra space using in-place index placement (value x should be placed at index x-1), with engineering mapping, pitfalls, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/25-reverse-nodes-in-k-group/Tue, 10 Feb 2026 10:25:53 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/25-reverse-nodes-in-k-group/Reverse a linked list in groups of k nodes in-place, leaving the last group unchanged if its size is smaller than k. This guide presents a dummy-node + kth-scan + in-place reversal template in O(n) time and O(1) extra space.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/143-reorder-list/Tue, 10 Feb 2026 09:57:31 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/143-reorder-list/Reorder a linked list to L0-&gt;Ln-&gt;L1-&gt;Ln-1... in O(n) time and O(1) extra space using split, reverse, and alternating merge, with derivation, pitfalls, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/92-reverse-linked-list-ii/Tue, 10 Feb 2026 09:56:14 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/92-reverse-linked-list-ii/Reverse only the interval [left, right] in a singly linked list using a dummy node and in-place head insertion. O(n) time, O(1) extra space, with derivation, pitfalls, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/141-linked-list-cycle/Tue, 10 Feb 2026 08:55:58 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/141-linked-list-cycle/Detect whether a singly linked list has a cycle using Floyd fast/slow pointers in O(n) time and O(1) extra space, with proof intuition, pitfalls, engineering mapping, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/234-palindrome-linked-list/Mon, 09 Feb 2026 17:38:32 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/234-palindrome-linked-list/Check whether a singly linked list is a palindrome in O(n) time and O(1) extra space: find middle with fast/slow pointers, reverse second half, compare, then restore list structure.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/206-reverse-linked-list/Mon, 09 Feb 2026 17:27:59 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/206-reverse-linked-list/Reverse a singly linked list in O(n) time and O(1) extra space with the three-pointer iterative template, with recursive comparison, engineering mapping, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/560-subarray-sum-equals-k/Mon, 09 Feb 2026 13:19:45 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/560-subarray-sum-equals-k/Count subarrays whose sum equals k in O(n) using prefix sum and frequency hash map, with engineering scenarios, pitfalls, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/160-intersection-of-two-linked-lists/Mon, 09 Feb 2026 09:26:37 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/160-intersection-of-two-linked-lists/Find the intersection node of two singly linked lists without modifying structure: two pointers switching heads synchronize in O(m+n) time and O(1) extra space, with derivation, engineering mapping, and multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/437-path-sum-iii/Wed, 04 Feb 2026 16:02:26 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/437-path-sum-iii/Count downward paths in a binary tree whose sum equals targetSum in O(n) using prefix sums and a frequency hash map, with derivation, engineering mapping, and multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/54-spiral-matrix/Tue, 03 Feb 2026 10:01:50 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/54-spiral-matrix/Traverse a matrix in clockwise spiral order in O(mn) using boundary shrinking. Includes engineering scenarios, pitfalls, and multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/42-trapping-rain-water/Sat, 24 Jan 2026 10:40:53 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/42-trapping-rain-water/Compute trapped rain water in O(n) using two pointers and left/right maxima. Includes engineering scenarios, pitfalls, and multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/53-maximum-subarray/Fri, 23 Jan 2026 13:21:02 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/53-maximum-subarray/Use Kadane&#39;s algorithm to compute the maximum subarray sum in O(n). Includes engineering scenarios, pitfalls, and multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/1437-check-if-all-ones-are-at-least-k-places-away/Thu, 22 Jan 2026 10:49:42 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/1437-check-if-all-ones-are-at-least-k-places-away/One-pass check to ensure all 1s are at least k apart. Includes engineering scenarios, pitfalls, and multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/231-power-of-two/Wed, 21 Jan 2026 14:06:56 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/231-power-of-two/Judge whether an integer is a power of two in O(1) time using bit tricks. Includes engineering scenarios, pitfalls, and multi-language solutions.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/1456-maximum-number-of-vowels-in-a-substring-of-given-length/Tue, 20 Jan 2026 13:40:45 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/1456-maximum-number-of-vowels-in-a-substring-of-given-length/Use a fixed-size sliding window to compute the maximum number of vowels in O(n). Includes engineering scenarios and multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/239-sliding-window-maximum/Mon, 19 Jan 2026 17:46:14 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/239-sliding-window-maximum/Solve Sliding Window Maximum in O(n) with a monotonic queue, including engineering scenarios, complexity comparisons, and multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/1512-number-of-good-pairs/Tue, 30 Dec 2025 11:40:00 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/1512-number-of-good-pairs/Solve Good Pairs with one-pass hash counting, plus engineering scenarios, complexity, and multi-language solutions.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/1-two-sum/Thu, 04 Dec 2025 11:10:00 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/1-two-sum/<h1 id="leetcode-1-two-sum">LeetCode 1: Two Sum</h1> <h2 id="summary">Summary</h2> <p>Find two indices such that <code>nums[i] + nums[j] = target</code>. Use a hash map for O(n) time.</p> <h2 id="approach">Approach</h2> <p>Iterate and store <code>value -&gt; index</code>. For each number <code>x</code>, check if <code>target - x</code> exists.</p> <h2 id="complexity">Complexity</h2> <ul> <li>Time: O(n)</li> <li>Space: O(n)</li> </ul> <h2 id="python-reference-implementation">Python reference implementation</h2> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-python" data-lang="python"><span style="display:flex;"><span><span style="color:#66d9ef">def</span> <span style="color:#a6e22e">two_sum</span>(nums, target): </span></span><span style="display:flex;"><span> seen <span style="color:#f92672">=</span> {} </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">for</span> i, x <span style="color:#f92672">in</span> enumerate(nums): </span></span><span style="display:flex;"><span> y <span style="color:#f92672">=</span> target <span style="color:#f92672">-</span> x </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">if</span> y <span style="color:#f92672">in</span> seen: </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">return</span> [seen[y], i] </span></span><span style="display:flex;"><span> seen[x] <span style="color:#f92672">=</span> i </span></span></code></pre></div>https://shio-chan-dev.github.io/jeanblog/alg/leetcode/2300-successful-pairs-of-spells-and-potions/Thu, 04 Dec 2025 11:10:00 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/2300-successful-pairs-of-spells-and-potions/<h1 id="leetcode-2300-successful-pairs-of-spells-and-potions">LeetCode 2300: Successful Pairs of Spells and Potions</h1> <h2 id="summary">Summary</h2> <p>For each spell, count how many potions make <code>spell * potion &gt;= success</code>. Sort potions and binary search the threshold.</p> <h2 id="approach">Approach</h2> <ul> <li>Sort potions.</li> <li>For each spell, compute <code>need = ceil(success / spell)</code>.</li> <li>Use binary search to find the first potion &gt;= need.</li> </ul> <h2 id="complexity">Complexity</h2> <ul> <li>Time: O(n log n)</li> <li>Space: O(1) extra (or O(n) if sorting a copy)</li> </ul> <h2 id="python-reference-implementation">Python reference implementation</h2> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-python" data-lang="python"><span style="display:flex;"><span><span style="color:#f92672">import</span> bisect </span></span><span style="display:flex;"><span><span style="color:#f92672">import</span> math </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span><span style="color:#66d9ef">def</span> <span style="color:#a6e22e">successful_pairs</span>(spells, potions, success): </span></span><span style="display:flex;"><span> potions <span style="color:#f92672">=</span> sorted(potions) </span></span><span style="display:flex;"><span> n <span style="color:#f92672">=</span> len(potions) </span></span><span style="display:flex;"><span> res <span style="color:#f92672">=</span> [] </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">for</span> s <span style="color:#f92672">in</span> spells: </span></span><span style="display:flex;"><span> need <span style="color:#f92672">=</span> (success <span style="color:#f92672">+</span> s <span style="color:#f92672">-</span> <span style="color:#ae81ff">1</span>) <span style="color:#f92672">//</span> s </span></span><span style="display:flex;"><span> idx <span style="color:#f92672">=</span> bisect<span style="color:#f92672">.</span>bisect_left(potions, need) </span></span><span style="display:flex;"><span> res<span style="color:#f92672">.</span>append(n <span style="color:#f92672">-</span> idx) </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">return</span> res </span></span></code></pre></div>https://shio-chan-dev.github.io/jeanblog/alg/leetcode/2379-minimum-recolors-to-get-k-consecutive-black-blocks/Thu, 04 Dec 2025 11:10:00 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/2379-minimum-recolors-to-get-k-consecutive-black-blocks/<h1 id="leetcode-2379-minimum-recolors-to-get-k-consecutive-black-blocks">LeetCode 2379: Minimum Recolors to Get K Consecutive Black Blocks</h1> <h2 id="summary">Summary</h2> <p>Given a string of &lsquo;B&rsquo; and &lsquo;W&rsquo;, find the minimum recolors to make a substring of length <code>k</code> all black.</p> <h2 id="approach">Approach</h2> <p>Use a sliding window of length <code>k</code> and count the number of whites in the window. The minimum whites across all windows is the answer.</p> <h2 id="complexity">Complexity</h2> <ul> <li>Time: O(n)</li> <li>Space: O(1)</li> </ul> <h2 id="python-reference-implementation">Python reference implementation</h2> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-python" data-lang="python"><span style="display:flex;"><span><span style="color:#66d9ef">def</span> <span style="color:#a6e22e">minimum_recolors</span>(blocks, k): </span></span><span style="display:flex;"><span> whites <span style="color:#f92672">=</span> sum(<span style="color:#ae81ff">1</span> <span style="color:#66d9ef">for</span> c <span style="color:#f92672">in</span> blocks[:k] <span style="color:#66d9ef">if</span> c <span style="color:#f92672">==</span> <span style="color:#e6db74">&#39;W&#39;</span>) </span></span><span style="display:flex;"><span> ans <span style="color:#f92672">=</span> whites </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">for</span> i <span style="color:#f92672">in</span> range(k, len(blocks)): </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">if</span> blocks[i<span style="color:#f92672">-</span>k] <span style="color:#f92672">==</span> <span style="color:#e6db74">&#39;W&#39;</span>: </span></span><span style="display:flex;"><span> whites <span style="color:#f92672">-=</span> <span style="color:#ae81ff">1</span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">if</span> blocks[i] <span style="color:#f92672">==</span> <span style="color:#e6db74">&#39;W&#39;</span>: </span></span><span style="display:flex;"><span> whites <span style="color:#f92672">+=</span> <span style="color:#ae81ff">1</span> </span></span><span style="display:flex;"><span> ans <span style="color:#f92672">=</span> min(ans, whites) </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">return</span> ans </span></span></code></pre></div>https://shio-chan-dev.github.io/jeanblog/alg/leetcode/2841-maximum-sum-of-almost-unique-subarray/Thu, 04 Dec 2025 11:10:00 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/2841-maximum-sum-of-almost-unique-subarray/<h1 id="leetcode-2841-maximum-sum-of-almost-unique-subarray">LeetCode 2841: Maximum Sum of Almost Unique Subarray</h1> <h2 id="summary">Summary</h2> <p>Given an array, window size <code>k</code>, and threshold <code>m</code>, find the maximum sum of any length-<code>k</code> subarray that contains at least <code>m</code> distinct elements.</p> <h2 id="approach">Approach</h2> <p>Use a sliding window with a frequency map, track window sum and number of distinct values.</p> <h2 id="complexity">Complexity</h2> <ul> <li>Time: O(n)</li> <li>Space: O(n) for frequency map</li> </ul> <h2 id="python-reference-implementation">Python reference implementation</h2> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-python" data-lang="python"><span style="display:flex;"><span><span style="color:#66d9ef">def</span> <span style="color:#a6e22e">max_sum_almost_unique</span>(nums, m, k): </span></span><span style="display:flex;"><span> <span style="color:#f92672">from</span> collections <span style="color:#f92672">import</span> defaultdict </span></span><span style="display:flex;"><span> count <span style="color:#f92672">=</span> defaultdict(int) </span></span><span style="display:flex;"><span> distinct <span style="color:#f92672">=</span> <span style="color:#ae81ff">0</span> </span></span><span style="display:flex;"><span> window_sum <span style="color:#f92672">=</span> <span style="color:#ae81ff">0</span> </span></span><span style="display:flex;"><span> ans <span style="color:#f92672">=</span> <span style="color:#ae81ff">0</span> </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">for</span> i, x <span style="color:#f92672">in</span> enumerate(nums): </span></span><span style="display:flex;"><span> window_sum <span style="color:#f92672">+=</span> x </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">if</span> count[x] <span style="color:#f92672">==</span> <span style="color:#ae81ff">0</span>: </span></span><span style="display:flex;"><span> distinct <span style="color:#f92672">+=</span> <span style="color:#ae81ff">1</span> </span></span><span style="display:flex;"><span> count[x] <span style="color:#f92672">+=</span> <span style="color:#ae81ff">1</span> </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">if</span> i <span style="color:#f92672">&gt;=</span> k: </span></span><span style="display:flex;"><span> y <span style="color:#f92672">=</span> nums[i <span style="color:#f92672">-</span> k] </span></span><span style="display:flex;"><span> window_sum <span style="color:#f92672">-=</span> y </span></span><span style="display:flex;"><span> count[y] <span style="color:#f92672">-=</span> <span style="color:#ae81ff">1</span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">if</span> count[y] <span style="color:#f92672">==</span> <span style="color:#ae81ff">0</span>: </span></span><span style="display:flex;"><span> distinct <span style="color:#f92672">-=</span> <span style="color:#ae81ff">1</span> </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">if</span> i <span style="color:#f92672">&gt;=</span> k <span style="color:#f92672">-</span> <span style="color:#ae81ff">1</span> <span style="color:#f92672">and</span> distinct <span style="color:#f92672">&gt;=</span> m: </span></span><span style="display:flex;"><span> ans <span style="color:#f92672">=</span> max(ans, window_sum) </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">return</span> ans </span></span></code></pre></div>