Leetcode

974. Subarray Sums Divisible by K Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Array、Hash Table、Prefix Sum 一、題目 Given an integer array nums and an integer k, return the number of non-empty subarrays that have a sum divisible by k. A subarray is a contiguous part of an array. Example 1: Input: nums = [4,5,0,-2,-3,1], k = 5 Output: 7 Explanation: There are 7 subarrays with a sum divisible by k = 5: [4, 5, 0, -2, -3, 1], [5], [5, 0], [5, 0, -2, -3], [0], [0, -2, -3], [-2, -3] Example 2:...

53. Maxmimum Subarray Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Array、Divide and Conquer、Dynamic Programming 一、題目 Given an integer array num, find the subarray with the largest sum, and return its sum. Example 1: Input: nums = [-2,1,-3,4,-1,2,1,-5,4] Output: 6 Explanation: The subarray [4,-1,2,1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: [5,4,-1,7,8] Output: 23 Explanation: The subarray [5,4,-1,7,8] has the largest sum 23....

918. Maximum Sum Circular Subarray Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Array、Divide and Conquer、Dynamic Programming、Queue、Monotonic Queue 一、題目 Given a circular integer array nums of length n, return the maximum possible sum of a non-empty subarray of nums. A circular array means the end of the array connects to the beginning of the array. Formally, the next element of nums[i] is nums[(i + 1) % n] and the previous element of nums[i] is nums[(i - 1 + n) % n]....

926. Flip String to Monotone Increasing Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: String、Dynamic Programming 一、題目 A binary string is monotone increasing if it consists of some number of 0’s (possibly none), followed by some number of 1’s (also possibly none). You are given a binary string s. You can flip s[i] changing 0 to 1 or from 1 to 0. Return the minimum number of flips to make s monotone increasing. Example 1:...

1519. Number of Nodes in the Sub-Tree With the Same Level Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Hash Table、Tree、Depth-First Search、Breadth-First Search、Counting 一、題目 You are given a tree (i.e. a connected, undirected graph that has no cycles) consisting of n nodes numbered from 0 to n - 1 and exactly n - 1 edges. The root of the tree is the node 0, and each node of the tree has a label which is a lower-case character given in the string labels (i....