Hot100

Subtitle / Summary Spiral traversal looks like “just printing in a fancy order”, but the real difficulty is getting boundaries and invariants right. This ACERS guide gives a reusable boundary-shrinking template and runnable multi-language solutions. Reading time: 12–15 min Tags: Hot100, matrix, simulation, boundary shrinking SEO keywords: Hot100, Spiral Matrix, clockwise traversal, boundary shrinking, LeetCode 54 Meta description: O(mn) spiral order traversal using boundary shrinking, with pitfalls, engineering scenarios, and runnable code. A — Algorithm Problem Restatement Given an m × n matrix matrix, return all elements in clockwise spiral order. ...

Problem Requirement You are given n non-negative integers in height. Each integer is the height of a bar with width 1, and all bars are adjacent from left to right. After rain, taller bars on both sides may hold water above shorter bars. Return the total amount of water trapped by the entire elevation map. LeetCode expects this interface: class Solution: def trap(self, height: List[int]) -> int: ... Example 1 Input: height = [0,1,0,2,1,0,1,3,2,1,2,1] Output: 6 Example 2 Input: height = [4,2,0,3,2,5] Output: 9 Constraints n == len(height) 1 <= n <= 2 * 10^4 0 <= height[i] <= 10^5 Step 1: First Answer How Much Water One Position Holds Do not calculate the whole elevation map yet. Focus on one position: ...

Subtitle / Summary Maximum Subarray is the classic 1D DP / greedy template. This ACERS guide explains Kadane’s idea, engineering use cases, and runnable multi-language solutions. Reading time: 10–12 min Tags: Hot100, dynamic programming, greedy SEO keywords: Maximum Subarray, Kadane, dynamic programming, O(n), Hot100 Meta description: Kadane O(n) maximum subarray sum with engineering scenarios and multi-language code. A — Algorithm Problem Restatement Given an integer array nums, find the contiguous subarray with the largest sum (must contain at least one element) and return the sum. ...