Hot100

Problem Requirement Given an encoded string s, return its decoded string. The encoding rule is: k[encoded_string] The encoded_string inside the brackets is repeated exactly k times, where k is a positive integer. Encodings may be nested or adjacent to ordinary lowercase letters. The problem guarantees that: The input is always valid, with matching brackets and no extra spaces. Original text contains no digits; digits only represent repeat counts. Inputs such as 3a or 2[4] do not occur. The decoded string length does not exceed 10^5. Examples Input Output "3[a]2[bc]" "aaabcbc" "3[a2[c]]" "accaccacc" "2[abc]3[cd]ef" "abcabccdcdcdef" Constraints 1 <= s.length <= 30 s contains only lowercase English letters, digits, and [] Every repeat count is in [1, 300] LeetCode provides this method signature: ...

Problem Requirement You are given a non-negative integer array heights. Each heights[i] is the height of a bar with width 1, and all bars are adjacent. Return the area of the largest rectangle that can be formed in the histogram. A legal rectangle covers a contiguous interval of bars. Its width is the number of bars in that interval, and its height cannot exceed the shortest bar in the interval. ...

Problem Requirement You are given a non-empty integer array nums. Exactly one element appears once. Every other element appears exactly twice. Return the element that appears once. LeetCode provides this method contract: singleNumber(nums: List[int]) -> int The solution must also satisfy two resource requirements: O(n) time O(1) extra space Example 1 Input: nums = [2,2,1] Output: 1 2 appears twice. Only 1 appears once. Example 2 Input: nums = [4,1,2,1,2] Output: 4 Both 1 and 2 have matching copies. Only 4 remains unpaired. ...

Problem Requirement Given a non-negative integer n, return an array answer of length n + 1. For every index: answer[i] = the number of 1 bits in the binary representation of i The requested range includes both 0 and n. LeetCode provides this method contract: countBits(n: int) -> List[int] Example 1 Input: n = 2 Output: [0,1,1] 0 -> 0 -> 0 set bits 1 -> 1 -> 1 set bit 2 -> 10 -> 1 set bit Example 2 Input: n = 5 Output: [0,1,1,2,1,2] Constraints 0 <= n <= 10^5 Step 1: This Time We Need Every Answer From 0 to n LeetCode 191 asks for one integer’s set-bit count. For n = 5, this problem asks for all six related answers: ...

Problem Requirement You are given an integer array temperatures, where temperatures[i] is the temperature on day i. Return an array answer where: answer[i] = the number of days after day i until a warmer temperature If no later day is warmer, answer[i] = 0. “Warmer” means strictly greater. An equal temperature does not resolve a waiting day. LeetCode provides this method contract: dailyTemperatures(temperatures: List[int]) -> List[int] Example Input: temperatures = [73,74,75,71,69,72,76,73] Output: [1,1,4,2,1,1,0,0] Constraints 1 <= temperatures.length <= 10^5 30 <= temperatures[i] <= 100 Step 1: The Answer Is a Waiting Time, Not a Temperature Start with a smaller input: ...

Subtitle / Summary Jump Game II is not just reachability. It asks how many coverage layers are needed to reach the last index. Reading time: 8-10 min Tags: Hot100, greedy, array, reachability boundary SEO keywords: LeetCode 45, Jump Game II, greedy, current_end, farthest, minimum jumps Meta description: A pressure-first Python guide to LeetCode 45 that derives the minimum-jump greedy scan from coverage layers. Problem Requirement You are given an integer array nums. ...

Subtitle / Summary Non-overlapping Intervals is easier when you stop asking which interval to delete first. First ask how many intervals can remain. Reading time: 8-10 min Tags: Hot100, greedy, intervals, sorting SEO keywords: LeetCode 435, Non-overlapping Intervals, greedy, interval greedy Meta description: A pressure-first Python guide to LeetCode 435 that derives minimum removals from maximum kept intervals and an earliest-ending greedy scan. Problem Requirement You are given an array of intervals intervals. ...

Subtitle / Summary A single arrow does not belong to one balloon. It belongs to a group of balloon intervals that share at least one x-position. Reading time: 9-11 min Tags: Hot100, greedy, intervals, sorting SEO keywords: LeetCode 452, Minimum Number of Arrows to Burst Balloons, greedy, interval greedy Meta description: A pressure-first Python guide to LeetCode 452 that derives shared intersections, an intersection-scanning baseline, and the final arrow position greedy. Problem Requirement You are given an array points. ...

Subtitle / Summary The greedy idea is not “buy low, sell high” as a slogan. The precise rule is: if today is the sell day, the best buy day must be the lowest price before today. Reading time: 8-10 min Tags: Hot100, greedy, array, stock SEO keywords: LeetCode 121, Best Time to Buy and Sell Stock, greedy, historical minimum price Meta description: A pressure-first Python guide to LeetCode 121 that derives brute force, historical minimum price, and the final one-pass greedy solution. Problem Requirement You are given an array prices, where prices[i] is the stock price on day i. ...

Subtitle / Summary Jump Game is not about guessing one path. It is about maintaining how far all reachable positions can cover. Reading time: 8-10 min Tags: Hot100, greedy, array, reachability SEO keywords: LeetCode 55, Jump Game, greedy, farthest reach, reachability Meta description: A pressure-first Python guide to LeetCode 55 that derives a reachable-array baseline and compresses it into the farthest reachable range. Problem Requirement You are given an integer array nums. ...