題號 題目 類別 題解 1 Two Sum Hash Table Hash Table 2 Add Two numbers Linked List Recursion 201 Bitwise AND of Numbers Range Bitwise Operation Lowbit = x&(~x+1) 204 Count Primes Math Thetory The Sieve of Eratosthenes 408 Valid Word Abbreviation Two Pointers 字串轉數字
132. Palindrome Partitioning II Hardness: \(\color{red}\textsf{Hard}\) Ralated Topics: string, dynamic programming 一、題目 Given a string s, partition s such that every substring of the partition is a palindrome. Return the minimum cuts needed for a palindrome partitioning of s. Example 1: Input: s = “aab” Output: 1 Explanation: The palindrome partitioning [“aa”, “b”] could be produced using 1 cut. Example 2: Input: s = “a” Output: 0 Example 3: Input: s = “ab” Output: 1 Constraints:...
491. Non-decreasing Subsequences Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Array、Hash Table、Backtracking、Bit Manipulation 一、題目 Given an integer array nums, return all the different possible non-decreasing subsequences of the given array with at least two elements. You may return the answer in any order. Example 1: Input: nums = [4,6,7,7] Output: [[4,6],[4,6,7],[4,6,7,7],[4,7],[4,7,7],[6,7],[6,7,7],[7,7]] Explanation: Example 2: Input: nums = [4,4,3,2,1] Output: [[4,4]] Constraints: <= nums.length <= 15 -100 <= nums[i] <= 100 二、分析 這一很典型的是一個 backtrack 的問題，只要熟悉回溯法的框架並注意終止條件與處理重覆子序列即可。 終止條件為 i == nums....
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....