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public static boolean isHappy(int n) { HashSet<Integer> al = new HashSet<Integer>(); while (n != 1) { n = func(n); if (!al.add(n)) return false;

public class Solution { public int[] singleNumber(int[] nums) { int []res=new int[2]; Arrays.sort(nums); int i=0,j=0; while(i<nums.length){ if(i<(nums.leng

N^N=0public class Solution { public int singleNumber(int[] nums) { int result = nums[0]; for (int i = 1; i < nums.length; i++) { result = result ^ nums[i]; }

除第一个数 1 外，所有的Ugly Number都是有较小的Ugly Number乘2，3，5得到的，所以本题的关键就是在 1*2，2*2，3*2，4*2，5*2，6*2，8*2… 1*3，2*3，3*3，4*3，5*3，6*3，8*3… 1*5，2*5，3*5，4*5，5*5，6*5，8*5… 之中找到第n个数。public static int nthUglyNumber(int n)

public boolean isUgly(int num) { if (num == 0)//不要忘记num=0的情况 return false; while (num % 2 == 0 || num % 3 == 0 || num % 5 == 0) { if (num % 2 == 0)

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public class Solution {

题目要求在O(n)时间和O(1)空间内判断一个链表是不是回文的。 先将链表分成2部分，然后反转其中一个，在进行比较。/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; }

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Sol

网上的public class Solution { public int[] productExceptSelf(int[] nums) { int[] res = new int[nums.length]; res[res.length-1] = 1; for(int i=nums.length-2; i>=0; i--) {

Implement atoi to convert a string to an integer.Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.N

Reverse digits of an integer.Example1: x = 123, return 321 Example2: x = -123, return -321Have you thought about this?Here are some good questions to ask before coding. Bonus points for you if you hav

The string “PAYPALISHIRING” is written in a zigzag（Z字形） pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)P A H NA P L S I

Given a string S, find the longest palindromic(adj. 回文的；复发的) substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.Tags:String提交

public int addDigits(int num) { while (num > 9) { num = func(num); } return num; } public static int func(int n) { int temp = 0; while (n > 0) {

public class Solution { public int singleNumber(int[] nums) { int res = 0; Arrays.sort(nums); for (int a : nums) System.out.println(a); int i = 0;

public class Solution { public List<List<String>> solveNQueens(int n) { int[]a=new int[n]; init(a); int i = 0, j = 0; List<List<String>>list=new ArrayList<List<S

1 TwoSum 4 Median of Two Sorted Arrays 5 Longest Palindromic Substring 6 ZigZag Conversion 7 Reverse Integer 8 String to Integer (atoi) 234 Palindrome Linked List 235 Lowest Common Ancestor o

public static String longestCommonPrefix(String[] strs) { if (strs.length == 0) return ""; for (int i = 0; i < strs[0].length(); i++) { for (int j = 1; j < strs.le

public static int romanToInt(String s) { String[] str = { "I", "V", "X", "L", "C", "D", "M" }; int[] nums = { 1, 5, 10, 50, 100, 500, 1000 }; Map<String, Integer> map = new HashMa

public static boolean isSameTree(TreeNode p, TreeNode q) { if (p == null) return q == null; if (q == null) return p == null; if ((p.left == null) && (p.rig

类似的题目有 1 TwoSum 15 3Sum 18 4Sumpublic static int threeSumClosest(int[] nums, int target) { Arrays.sort(nums); int minMinus = 10000; int result = 0; int sum = 0;

import java.util.ArrayList;import java.util.Arrays;import java.util.List;public class No15 { public static void main(String[] args) { int[] nums = { -1, 0, 1, 2, -1, -4 }; System.o

第一次使用的是笨办法，四层嵌套for循环，总是超时public static List<List<Integer>> fourSum(int[] nums, int target) { List<List<Integer>> result = new ArrayList<List<Integer>>(); Arrays.sort(nums); for (

public class No11 { public static void main(String[] args) { int[] height = { 3, 4, 5 ,3}; System.out.println(maxArea(height)); } public static int maxArea(int[] height) {

public class No10 { public static void main(String[] args) { System.out.println(isMatch("aa", "a")); System.out.println(isMatch("aa", "aa")); System.out.println(isMatch("aaa"

罗马数字的规则 基本字符 I V X L C D M 对应的数字 1 5 10 50 100 500 1000相同的数字连写、所表示的数等于这些数字相加得到的数、如：Ⅲ=3；小的数字在大的数字的右边、所表示的数等于这些数字相加得到的数、 如：Ⅷ=8、Ⅻ=12；小的数字、（限于 Ⅰ、X 和 C）在大的数字的左边、所表示的数等于大数减小数

“` public static boolean isValidSudoku(char[][] board) { Set<Character> set = new HashSet<Character>(); for (int i = 0; i < 9; i++) { set.clear(); for (int j = 0; j < 9; j++) {

public static int kthSmallest(TreeNode root, int k) { Stack<TreeNode>stack=new Stack<>(); TreeNode n= root; while(n!=null){ stack.push(n); n=n.left;

位运算public class Solution { public boolean isPowerOfTwo(int n) { return n > 0 && ((n & (n - 1)) == 0 ); } }

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)).提交超时，偶尔一次提交能通过。public class No