Xd_Yu的专栏

Given an array of integers A and let n to be its length.Assume Bk to be an array obtained by rotating the array A k positions clock-wise, we define a “rotation function” F on A as follow:F(k) = 0 * Bk[

Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).For example: Given binary tree [3,9,20,null,null,15,7], 3 / \ 9 20 /

Given a binary tree, return the bottom-up level order traversal of its nodes’ values. (ie, from left to right, level by level from leaf to root).For example: Given binary tree [3,9,20,null,null,15,7],

Given an index k, return the kth row of the Pascal’s triangle.For example, given k = 3, Return [1,3,3,1].public class Solution { public List<Integer> getRow(int rowIndex) { List<List<Inte

Implement the following operations of a stack using queues.push(x) – Push element x onto stack. pop() – Removes the element on top of the stack. top() – Get the top element. empty() – Return whether

Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].Solve it without division and in O(n).For e

Given a positive integer, return its corresponding column title as appear in an Excel sheet.For example: 1 -> A 2 -> B 3 -> C ... 26 -> Z 27 -> AA 28 -> AB public class Solut

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.Example:Given nums = [-2, 0, 3, -5, 2, -1]sumRange(0, 2) -> 1sumRange(2, 5) -> -1sumRange(0, 5) ->

You are a product manager and currently leading a team to develop a new product. Unfortunately, the latest version of your product fails the quality check. Since each version is developed based on the

Given numRows, generate the first numRows of Pascal’s triangle.For example, given numRows = 5, Return[ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1]]public class Solution { public Li

You are playing the following Bulls and Cows game with your friend: You write down a number and ask your friend to guess what the number is. Each time your friend makes a guess, you provide a hint that

You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.For example: Given the below binary tree and sum = 2

Reverse a singly linked list.用三个节点保存前、中、后三个接口即可。/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */p

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).For example, this binary tree [1,2,2,3,4,4,3] is symmetric: 1 / \ 2 2 / \ / \3 4 4 3But the f

Given an integer, write a function to determine if it is a power of two.这道题让我们判断一个数是否为2的次方数，而且要求时间和空间复杂度都为常数，那么对于这种玩数字的题，我们应该首先考虑位操作 Bit Operation。在LeetCode中，位操作的题有很多，比如比如Repeated DNA Sequences 求重复的DNA

Given an integer, write a function to determine if it is a power of three. Follow up: Could you do it without using any loop / recursion? 这道题让我们判断一个数是不是3的次方数，在LeetCode中，有一道类似的题目Power of Two，那道题有个非常简

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.Example: Given num = 16, return true. Given num = 5, return false.Follow up: Could you solve it without loops/re

Given a non-negative number represented as an array of digits, plus one to the number.The digits are stored such that the most significant digit is at the head of the list.细节比较繁琐，感觉没啥技术含量。public class

We are playing the Guess Game. The game is as follows: I pick a number from 1 to n. You have to gue-1 : My number is lower 1 : My number is higher 0 : Congrats! You got it!Example:n = 10, I pick 6.R

Compare two version numbers version1 and version2. If version1 > version2 return 1, if version1 < version2 return -1, otherwise return 0.You may assume that the version strings are non-empty and conta

Given a positive integer n, break it into the sum of at least two positive integers and maximize the product of those integers. Return the maximum product you can get.For example, given n = 2, return 1

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.Note: You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold additional

Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the difference between i and j is at most k.用hashMap

假设有一个数组，它的第i个元素是一个给定的股票在第i天的价格。设计一个算法来找到最大的利润。你可以完成尽可能多的交易(多次买卖股票)。然而,你不能同时参与多个交易(你必须在再次购买前出售股票)。 解题思路 在Best Time to Buy and Sell Stock系列中，和本题最像的是Best Time to Buy and Sell Stock IV Best Time to Buy

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.For example, given the following triangle [ [2], [3,4], [6,5,

Create Maximum Number 题目描述Given two arrays of length m and n with digits 0-9 representing two numbers. Create the maximum number of length k <= m + n from digits of the two. The relative order of the

Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.Note: The solution set must not contain duplic

Given an array of integers, every element appears twice except for one. Find that single one.第一种解法就是《剑指offer》上的，下面是一种通用的解法：public class Solution { public static int singleNumber(int[] nums) {

Given a non-empty array of integers, return the k most frequent elements.For example, Given [1,1,1,2,2,3] and k = 2, return [1,2].用桶排序来做最后处理。public class Solution { public List<Integer> topKFreque

Given an array containing n distinct numbers taken from 0, 1, 2, …, n, find the one that is missing from the array.For example, Given nums = [0, 1, 3] return 2.解法一：（用等差数列的做法）public class Solution {

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.Example: Given nums = [2, 7, 11,

Java的子类不能获得父类的构造器，但在子类构造器中可以调用父类构造器的初始化代码。严格讲，Java类只能有一个父类，这种说法是错误的，应该换成如下说法：Java类只能有一个直接父类。实际上，Java可以有无限多个间接父类。如果在构造器中使用super，则super用于限定该构造器初始化的是该对象从父类继承得到的实例变量，而不是该类自己定义的实例变量。在继承中，实例变量也会发生类似于函数覆盖的

Description:Count the number of prime numbers less than a non-negative number, n.厄拉多塞筛法public class Solution { public int countPrimes(int n) { int[] res=new int[n]; int count=0;

Implement strStr().Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.解法一：（暴力法）public class Solution { public static int strStr(String haystack

题目描述操作给定的二叉树，将其变换为源二叉树的镜像。 输入描述:二叉树的镜像定义：源二叉树 8 / \ 6 10 / \ / \ 5 7 9 11 镜像二叉树 8 / \ 10

Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, fin

Given a linked list, determine if it has a cycle in it.Follow up: Can you solve it without using extra space?解法一：不用任何额外空间去做。/** * Definition for singly-linked list. * class ListNode { * int val

Given a linked list, return the node where the cycle begins. If there is no cycle, return null.《程序员面试金典》原题/** * Definition for singly-linked list. * class ListNode { * int val; * ListNode n

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.合并链表。/** * Definition for singly-linked list. * public cla