268. 缺失数字 给定一个包含 0, 1, 2, -, n 中 n 个数的序列,找出 0 - n 中没有出现在序列中的那个数. 示例 1: 输入: [3,0,1] 输出: 2 示例 2: 输入: [9,6,4,2,3,5,7,0,1] 输出: 8 说明: 你的算法应具有线性时间复杂度.你能否仅使用额外常数空间来实现? PS:位运算 class Solution { public int missingNumber(int[] nums) { int res = nums.length; for…

给定一个包含 0, 1, 2, ..., n 中 n 个数的序列,找出 0 .. n 中没有出现在序列中的那个数. 示例 1: 输入: [3,0,1] 输出: 2 示例 2: 输入: [9,6,4,2,3,5,7,0,1] 输出: 8 说明: 你的算法应具有线性时间复杂度.你能否仅使用额外常数空间来实现? 思路 因为给定的序列也是从0开始,所以可以进行排序,比较索引和索引对应的值,如果两个不等于说明就确实一个值了,还要注意一个情况是,没出现的数字是n 代码 class Solution(obje…

给定一个包含 0, 1, 2, ..., n 中 n 个数的序列,找出 0 .. n 中没有出现在序列中的那个数. 示例 1: 输入: [3,0,1] 输出: 2 示例 2: 输入: [9,6,4,2,3,5,7,0,1] 输出: 8 说明:你的算法应具有线性时间复杂度.你能否仅使用额外常数空间来实现? 思路有两种,一种是求和,根据数学方法算出缺失项,一种是使用异或,求出缺失项. 摘自评论区: 好像和以前的一道题(只出现一次的数字)有异曲同工之处.看了大家的题解,异或操作(^)是一种很好的方式,…

788. 旋转数字 我们称一个数 X 为好数, 如果它的每位数字逐个地被旋转 180 度后,我们仍可以得到一个有效的,且和 X 不同的数.要求每位数字都要被旋转. 如果一个数的每位数字被旋转以后仍然还是一个数字, 则这个数是有效的.0, 1, 和 8 被旋转后仍然是它们自己:2 和 5 可以互相旋转成对方(在这种情况下,它们以不同的方向旋转,换句话说,2 和 5 互为镜像):6 和 9 同理,除了这些以外其他的数字旋转以后都不再是有效的数字. 现在我们有一个正整数 N, 计算从 1 到 N 中有…

375. 猜数字大小 II 我们正在玩一个猜数游戏,游戏规则如下: 我从 1 到 n 之间选择一个数字,你来猜我选了哪个数字. 每次你猜错了,我都会告诉你,我选的数字比你的大了或者小了. 然而,当你猜了数字 x 并且猜错了的时候,你需要支付金额为 x 的现金.直到你猜到我选的数字,你才算赢得了这个游戏. 示例: n = 10, 我选择了8. 第一轮: 你猜我选择的数字是5,我会告诉你,我的数字更大一些,然后你需要支付5块. 第二轮: 你猜是7,我告诉你,我的数字更大一些,你支付7块. 第三轮:…

374. 猜数字大小 我们正在玩一个猜数字游戏. 游戏规则如下: 我从 1 到 n 选择一个数字. 你需要猜我选择了哪个数字. 每次你猜错了,我会告诉你这个数字是大了还是小了. 你调用一个预先定义好的接口 guess(int num),它会返回 3 个可能的结果(-1,1 或 0): -1 : 我的数字比较小 1 : 我的数字比较大 0 : 恭喜!你猜对了! 示例 : 输入: n = 10, pick = 6 输出: 6 PS: 强烈建议力扣换一个描述的,这个题描述的,简直是---- 我的数字指…

299. 猜数字游戏 你正在和你的朋友玩 猜数字(Bulls and Cows)游戏:你写下一个数字让你的朋友猜.每次他猜测后,你给他一个提示,告诉他有多少位数字和确切位置都猜对了(称为"Bulls", 公牛),有多少位数字猜对了但是位置不对(称为"Cows", 奶牛).你的朋友将会根据提示继续猜,直到猜出秘密数字. 请写出一个根据秘密数字和朋友的猜测数返回提示的函数,用 A 表示公牛,用 B 表示奶牛. 请注意秘密数字和朋友的猜测数都可能含有重复数字. 示例 1:…

41. 缺失的第一个正数 给定一个未排序的整数数组,找出其中没有出现的最小的正整数. 示例 1: 输入: [1,2,0] 输出: 3 示例 2: 输入: [3,4,-1,1] 输出: 2 示例 3: 输入: [7,8,9,11,12] 输出: 1 说明: 你的算法的时间复杂度应为O(n),并且只能使用常数级别的空间. class Solution { public int firstMissingPositive(int[] nums) { int[] m = new int[nums.leng…

268.缺失数字 描述 给定一个包含 0, 1, 2, ..., n 中 n 个数的序列,找出 0 .. n 中没有出现在序列中的那个数. 示例 示例 1: 输入: [3,0,1] 输出: 2 示例 2: 输入: [9,6,4,2,3,5,7,0,1] 输出: 8 说明: 你的算法应具有线性时间复杂度.你能否仅使用额外常数空间来实现? 思路 最直观的思路是对数据进行排序, 然后依次扫描, 便能找出漏掉的数字, 但是基于比较的排序算法的时间复杂度至少是 nlog(n) , 不满足题目要求. 思路一…

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array. Example 1 Input: [3,0,1] Output: 2 Example 2 Input: [9,6,4,2,3,5,7,0,1] Output: 8 Note:Your algorithm should run in linear runtime c…

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LeetCode:缺失的第一个正数[41] 题目描述 给定一个未排序的整数数组,找出其中没有出现的最小的正整数. 示例 1: 输入: [1,2,0] 输出: 3示例 2: 输入: [3,4,-1,1] 输出: 2示例 3: 输入: [7,8,9,11,12] 输出: 1说明: 你的算法的时间复杂度应为O(n),并且只能使用常数级别的空间. 题目分析 参照链接:https://leetcode-cn.com/problems/first-missing-positive/solution/tong…

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers. Ensure that numbers within the set are sorted in ascending order. Example 1…

Given a string S, you are allowed to convert it to a palindrome by adding characters in front of it. Find and return the shortest palindrome you can find by performing this transformation. For example: Given "aacecaaa", return "aaacecaaa&qu…

Given a 2D board and a list of words from the dictionary, find all words in the board. Each word must be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same le…

Design a data structure that supports the following two operations: void addWord(word)bool search(word) search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.…

There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: [0,1] Given the total number of courses and a l…

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by…

Say you have an array for which the ith element is the price of a given stock on day i. Design an algorithm to find the maximum profit. You may complete at most k transactions. 解题思路: https://leetcode.com/discuss/18330/is-it-best-solution-with-o-n-o-1…

Suppose a sorted array 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). Find the minimum element. The array may contain duplicates. 解题思路: 参考Java for LeetCode 081 Search in Rotated Sorted Array II J…

Suppose a sorted array 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). Find the minimum element. You may assume no duplicate exists in the array. 解题思路: 本题和Java for LeetCode 033 Search in Rotated S…

The set [1,2,3,…,n] contains a total of n! unique permutations. By listing and labeling all of the permutations in order, We get the following sequence (ie, for n = 3): "123" "132" "213" "231" "312" "…

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order. For example, Given n = 3, You should return the following matrix: [ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ]] 解题思路: 参考Java for LeetCode 054 Spiral Matrix,修改下…

Given a set of non-overlapping intervals, insert a new interval into the intervals (merge if necessary). You may assume that the intervals were initially sorted according to their start times. Example 1: Given intervals [1,3],[6,9], insert and merge…

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. Determine if you are able to reach the last index. For example: A =…

Given a collection of numbers that might contain duplicates, return all possible unique permutations. For example, [1,1,2] have the following unique permutations: [1,1,2], [1,2,1], and [2,1,1]. 解题思路一: 发现Java for LeetCode 046 Permutations自己想多了,代码直接拿来用…

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). The function p…

Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring. For "(()", the longest valid parentheses substring is "()", which has length = 2. Another example is &…

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity. 解题思路一: 之前我们有mergeTwoLists(ListNode l1, ListNode l2)方法,直接调用的话,需要k-1次调用,每次调用都需要产生一个ListNode[],空间开销很大.如果采用分治的思想,对相邻的两个ListNode进行mergeTwoLists,每次将规模减少一半,直到…

java java中将数字转换成字符非常方便,只要用一个"+"然后在跟一个空格行了.比如,你输入一个122 ,就会变成"122 ". import java.util.Scanner; public class God { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); int num; num=scanner.nextInt(); System.o…