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1、题目找出所有相加之和为 n 的 k 个数的组合。组合中只允许含有 1 - 9 的正整数，并且每种组合中不存在重复的数字。说明： 所有数字都是正整数。 解集不能包含重复的组合。示例 1:输入: k = 3, n = 7输出: [[1,2,4]]示例 2:输入: k = 3, n = 9输出: [[1,2,6], [1,3,5], [2,3,4]]来源：力扣（LeetCode）链接：https://leetcode-cn.com/problems/comb...

1、题目给定一个数组 candidates 和一个目标数 target ，找出 candidates 中所有可以使数字和为 target 的组合。candidates 中的每个数字在每个组合中只能使用一次。说明： 所有数字（包括目标数）都是正整数。 解集不能包含重复的组合。示例 1:输入: candidates = [10,1,2,7,6,1,5], target = 8,所求解集为:[ [1, 7], [1, 2, 5], [2, 6], [1, ...

1、题目给定一个无重复元素的数组 candidates 和一个目标数 target ，找出 candidates 中所有可以使数字和为 target 的组合。candidates 中的数字可以无限制重复被选取。说明： 所有数字（包括 target）都是正整数。 解集不能包含重复的组合。示例 1：输入：candidates = [2,3,6,7], target = 7,所求解集为：[ [7], [2,2,3]]示例 2：输入：candidates ...

1、题目给定两个整数 n 和 k，返回 1 ... n 中所有可能的 k 个数的组合。示例:输入: n = 4, k = 2输出:[ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4],]来源：力扣（LeetCode）链接：https://leetcode-cn.com/problems/combinations著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。2、思路：既可以使用动态规划，也可以用D...

1、题目给出集合 [1,2,3,…,n]，其所有元素共有 n! 种排列。按大小顺序列出所有排列情况，并一一标记，当 n = 3 时, 所有排列如下： "123" "132" "213" "231" "312" "321"给定 n 和 k，返回第 k 个排列。说明： 给定 n 的范围是 [1, 9]。 给定 k 的范围是[1, n!]。示例 1:输入: n = 3, k = 3输出: "213"示例 2:输...

题目：Given a non-empty array of digits representing a non-negative integer, plus one to the integer.The digits are stored such that the most significant digit is at the head of the list, and each el...

题目：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]]题意：给出数组元素（有重复元素）的全...

题目：Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.You may assume no duplicates in the arr...

题目：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 candidate...

题目：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 r...

题目：Given an array of strings, group anagrams together.Example:Input: ["eat", "tea", "tan", "ate", "nat", "bat"],Output:[ ["ate","eat","tea"], ["nat&

题目：You are given an n x n 2D matrix representing an image.Rotate the image by 90 degrees (clockwise).Note:You have to rotate the image in-place, which means you have to modify the input 2D mat...

题目：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 ...

题目：The count-and-say sequence is the sequence of integers with the first five terms as following:1. 12. 113. 214. 12115. 1112211 is read off as "one 1" or 11.11 is read...

题目：Given a set of distinct integers, nums, return all possible subsets (the power set).Note: The solution set must not contain duplicate subsets.Example:Input: nums = [1,2,3]Output:[ [3],...

题目：Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string.If the last word does not exist, return 0.Note: A word is ...

题目：Given two binary strings, return their sum (also a binary string).The input strings are both non-empty and contains only characters 1 or 0.Example 1:Input: a = "11", b = "1"Output: "100"...

题目：You are climbing a stair case. It takes n steps to reach to the top.Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?Note: Given n will be a pos...

题目：Implement int sqrt(int x).Compute and return the square root of x, where x is guaranteed to be a non-negative integer.Since the return type is an integer, the decimal digits are truncated and...

题目：Given a sorted linked list, delete all duplicates such that each element appear only once.Example 1:Input: 1->1->2Output: 1->2Example 2:Input: 1->1->2->3->3Outpu...

题目：A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).The robot can only move either down or right at any point in time. The robot is trying to reach t...

题目：Implement strStr().Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.Example 1:Input: haystack = "hello", needle = "ll"Output: 2Ex...

题目：Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.Example:Input: [-2,1,-3,4,-1,2,1,-5,4],Output: 6Expl...

题目：Given an array nums and a value val, remove all instances of that value in-place and return the new length.Do not allocate extra space for another array, you must do this by modifying the input...

题目：You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and ret...

题目：Write a function to find the longest common prefix string amongst an array of strings.If there is no common prefix, return an empty string "".Example 1:Input: ["flower","flow","flight"]Ou...

题目：Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent.A mapping of digit to letters (just like on the telephone buttons) i...

题目：Implement atoi which converts a string to an integer.The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting fro...

题目：Given an array of integers, return indices of the two numbers such that they add up to a specific target.You may assume that each input would have exactly one solution, and you may not use the ...

题目：Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.Symbol ValueI 1V 5X 10L 50C 100D ...

题目：Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.Example 1:Input: 121Output: trueExample 2:Input: -121Output: false...

题目：Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.Symbol ValueI 1V 5X 10L 50C 100D ...

题目：Given a 32-bit signed integer, reverse digits of an integer.Example 1:Input: 123Output: 321Example 2:Input: -123Output: -321Example 3:Input: 120Output: 21Note:Assume we ar...

题目：Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.For example, given n = 3, a solution set is:[ "((()))", "(()())", "(())()", "()...

题目：There are two sorted arrays nums1 and nums2 of size m and n respectively.Find the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)).You may assume nums1 ...

题目：Given a linked list, remove the n-th node from the end of list and return its head.Example:Given linked list: 1->2->3->4->5, and n = 2.After removing the second node from the e...

题目：Given n non-negative integers a1, a2, ..., an , where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of line i is at (i, ai) and (i, 0). Fin...

题目：Given a sorted array nums, remove the duplicates in-place such that each element appear only once and return the new length.Do not allocate extra space for another array, you must do this by mo...

题目：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]]题意：给出数组的全排列...

题目：Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.An input string is valid if:Open brackets must be closed by the same type...