Yjl_Richard的博客

题目描述给出集合 [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!]。样例示例 1:输入: n = 3, k = 3输出: “213”示例 2:输入: n = 4, k = 9输出: “2314”分析题目理解起来很简单

题目描述给定一个正整数 n，生成一个包含 1 到 n2n^2n2 所有元素，且元素按顺时针顺序螺旋排列的正方形矩阵。样例示例:输入: 3输出:[[ 1, 2, 3 ],[ 8, 9, 4 ],[ 7, 6, 5 ]]分析这是经典的数组题，题目看起来简单，但做起来的时候，很容易因为边界的问题搞到自己十分混乱。这里我推荐一下我的做法，首先是按圈来排列数字，然后把一圈拆成四个步骤，现实从左到右，然后再从上到下，再从右到左，最后从下到上这样按顺序的四步，完成一圈。按这样的顺序走，出错的概率就

题目描述给定一个仅包含大小写字母和空格 ’ ’ 的字符串 s，返回其最后一个单词的长度。如果字符串从左向右滚动显示，那么最后一个单词就是最后出现的单词。如果不存在最后一个单词，请返回 0 。说明：一个单词是指仅由字母组成、不包含任何空格字符的 最大子字符串。样例示例:输入: “Hello World”输出: 5分析这是一道简单的字符串分析题，翻译题意就是找到最后一个不含空格的字符串子串长度，建议从后往前遍历，先将后置空格给跳过以后，直到下一个空格的位置就是最后一个不含空格的字符串子串长度。

题目描述给出一个无重叠的 ，按照区间起始端点排序的区间列表。在列表中插入一个新的区间，你需要确保列表中的区间仍然有序且不重叠（如果有必要的话，可以合并区间）。样例示例 1：输入：intervals = [[1,3],[6,9]], newInterval = [2,5]输出：[[1,5],[6,9]]示例 2：输入：intervals = [[1,2],[3,5],[6,7],[8,10],[12,16]], newInterval = [4,8]输出：[[1,2],[3,10],[12,

题目描述给出一个区间的集合，请合并所有重叠的区间。样例示例 1:输入: intervals = [[1,3],[2,6],[8,10],[15,18]]输出: [[1,6],[8,10],[15,18]]解释: 区间 [1,3] 和 [2,6] 重叠, 将它们合并为 [1,6].示例 2:输入: intervals = [[1,4],[4,5]]输出: [[1,5]]解释: 区间 [1,4] 和 [4,5] 可被视为重叠区间。提示intervals[i][0] <= inter

DescriptionGiven a collection of distinct integers, return all possible permutations.ExampleInput: [1,2,3] Output: [ [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1] ]...

DescriptionGiven 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.Th...

DescriptionGiven 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 c...

DescriptionGiven an unsorted integer array, find the smallest missing positive integer.ExampleExample 1:Input: [1,2,0] Output: 3 Example 2:Input: [3,4,-1,1] Output: 2 Example 3:Input...

DescriptionThe count-and-say sequence is the sequence of integers with the first five terms as following:111211211111221 1 is read off as “one 1” or 11. 11 is read off as “two 1s” or 21. 2...

DescriptionWrite a program to solve a Sudoku puzzle by filling the empty cells.A sudoku solution must satisfy all of the following rules:Each of the digits 1-9 must occur exactly once in each ro...

DescriptionDetermine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:Each row must contain the digits 1-9 without repetition. Each colu...

DescriptionGiven 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...

DescriptionGiven an array of integers nums sorted in ascending order, find the starting and ending position of a given target value.Your algorithm’s runtime complexity must be in the order of O(lo...

DescriptionSuppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.(i.e., [0,1,2,4,5,6,7] might become [4,5,6,7,0,1,2]).You are given a target value to sear...

DescriptionGiven a string containing just the characters ‘(’ and ‘)’, find the length of the longest valid (well-formed) parentheses substring.ExampleExample 1:Input: “(()” Output: 2 Explana...

DescriptionGiven 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 repres...

DescriptionGiven two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.ExampleExample 1:Input: num1 = “2”, num2 = “3...

DescriptionGiven 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 (...

DescriptionGiven 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.Deter...

DescriptionGiven a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.ExampleExample 1:Input:[[ 1, 2, 3 ],[ 4, 5, 6 ],[ 7, 8, 9 ]]Output: [1,2,3,...

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

DescriptionThe n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.Given an integer n, return the number of distinct solutions to the n...

DescriptionThe n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.Given an integer n, return all distinct solutions to the n-queens pu...

DescriptionImplement pow(x, n), which calculates x raised to the power n (xn).ExampleExample 1:Input: 2.00000, 10 Output: 1024.00000 Example 2:Input: 2.10000, 3 Output: 9.26100 Example 3...

DescriptionGiven an array of strings, group anagrams together.ExampleInput: [“eat”, “tea”, “tan”, “ate”, “nat”, “bat”], Output: [ [“ate”,”eat”,”tea”], [“nat”,”tan”], [“bat”] ]N...

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

DescriptionGiven a collection of numbers that might contain duplicates, return all possible unique permutations.ExampleInput: [1,1,2] Output: [ [1,1,2], [1,2,1], [2,1,1] ]Analyse...

DescriptionGiven 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.Yo...

DescriptionImplement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.If such arrangement is not possible, it must rearrange it as the lowe...

DescriptionYou are given a string, s, and a list of words, words, that are all of the same length. Find all starting indices of substring(s) in s that is a concatenation of each word in words exactl...

8.15 Show that the following problem is NP-complete.

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

Given a linked list, remove the nth node from the end of list and return its head.

Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Given a digit string, return all possible letter combinations that the number could represent.

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers.