Hi, I'm Louislan ! 👋🏼

题目地址 https://leetcode.com/problems/permutations-ii/ 题目描述 Given a collection of numbers that might contain duplicates, return all possible unique permutations. Example: Input: [1,1,2] Output: [ [1,1,2], [1,2,1], [2,1,1] ] 思路 这道题是之前那道 Permutations 的延伸，由于输入数组有可能出现重复数字，如果按照之前的算法运算，会有重复排列产生，我们要避免重复的产生，在递归函数中要判断前面一个数和当前的数是否相等，如果相等，且其对应的 visited 中的值为 1，当前的数字才能使用（下文中会解释这样做的原因），否则需要跳过，这样就不会产生重复排列了，代码如下： 解法一： class Solution { public: vector<vector<int>> permuteUnique(vector<int>& nu....

题目地址 https://leetcode.com/problems/permutations/ 题目描述 Given a collection of distinct integers, return all possible permutations. Example: Input: [1,2,3] Output: [ [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1] ] 思路 这道题是求全排列问题，给的输入数组没有重复项，这跟之前的那道 Combinations 和类似，解法基本相同，但是不同点在于那道不同的数字顺序只算一种，是一道典型的组合题，而此题是求全排列问题，还是用递归 DFS 来求解。这里需要用到一个 visited 数组来标记某个数字是否访问过，然后在 DFS 递归函数从的循环应从头开始，而不是从 level 开始，这是和 Combinations 不同的地方，其余思路大体相同。这里再说下 level 吧，其本质是记录当前已经拼出的个数，一旦其达到了 nums 数组的长度，说明此时已经是一个全排列了，因为再加数....

题目地址 https://leetcode.com/problems/jump-game-ii/ 题目描述 Given an array of non-negative integers, you are initially positioned at the first index of the array. Each element in the array represents your maximum jump length at that position. Your goal is to reach the last index in the minimum number of jumps. Example: Input: [2,3,1,1,4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1, then 3 steps to the last index. Note: You can assume ....

题目地址 https://leetcode.com/problems/wildcard-matching/ 题目描述 Given an input string (s) and a pattern (p), implement wildcard pattern matching with support for '?' and '*'. '?' Matches any single character. '*' Matches any sequence of characters (including the empty sequence). The matching should cover the entire input string (not partial). Note: s could be empty and contains only lowercase letters a-z. p could be empty and contains only lowercase letters a-z, and characters like ? or *. Example....

题目地址 https://leetcode.com/problems/multiply-strings/ 题目描述 Given two non-negative integers num1 and num2represented as strings, return the product of num1 and num2, also represented as a string. Example 1: Input: num1 = "2", num2 = "3" Output: "6" Example 2: Input: num1 = "123", num2 = "456" Output: "56088" Note: The length of both num1 and num2 is < 110. Both num1 and num2 contain only digits 0-9. Both num1 and num2 do not contain any leading zero, except the number 0 itself. You must not ....

题目地址 https://leetcode.com/problems/trapping-rain-water/ 题目描述 Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining. The above elevation map is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped. Thanks Marcos for contributing this image! Example: Input: [0,1,0,2,1,0,1,3,2,1,2,1] Output: 6 思路 这道收集雨水的题跟之前的那道 Largest Rectangle in Histogr....

题目地址 https://leetcode.com/problems/first-missing-positive/ 题目描述 Given an unsorted integer array, find the smallest missing positive integer. Example 1: Input: [1,2,0] Output: 3 Example 2: Input: [3,4,-1,1] Output: 2 Example 3: Input: [7,8,9,11,12] Output: 1 Note: Your algorithm should run in O ( n ) time and uses constant extra space. 思路 这道题让我们找缺失的首个正数，由于限定了 O(n) 的时间，所以一般的排序方法都不能用，最开始博主没有看到还限制了空间复杂度，所以想到了用 HashSet 来解，这个思路很简单，把所有的数都存入 HashSet 中，然后循环从 1 开始递增找数字，哪个数字找不到就返回哪个数字，如果一直找到了最大的数字（这里是 n....

? 我在做什么？ 果然，人都是有惰性的啊，这才坚持几天我就不想继续做下去了，也不是说不想做下去，就今天感觉没有那个心情继续。。 感觉潜意识里把他当成了一个任务，而不是自己想做的一件事情。 果然还是懒惰在犯罪。 少坚持一天，离放弃还有多远呢。 今天的任务不完成，我就..

题目地址 https://leetcode.com/problems/combination-sum-ii/ 题目描述 Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target. Each number in candidates may only be used once in the combination. Note: All numbers (including target) will be positive integers. The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10,1,2,7,6,1,5], target = 8, A solution set is....

题目地址 https://leetcode.com/problems/combination-sum 题目描述 Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target. The same repeated number may be chosen from candidates unlimited number of times. Note: All numbers (including target) will be positive integers. The solution set must not contain duplicate combinations. Example 1: Input: candidates = [2,3,6,7], target = 7, ....