yanrui92的专栏

public boolean isPalindrome(int x) { if(x<0)return false; int y=0; int z=x; while(z>0){ int cur=z%10; y=y*10+cur; z=z/10; }

A peak element is an element that is greater than its neighbors. Given an input array where num[i] ≠ num[i+1], find a peak element and return its index. The array may contain multiple peaks, i

Climbing Stairs  Total Accepted: 36520 Total Submissions: 107274My Submissions Question  Solution  You are climbing a stair case. It takes n steps to reach to the top. Each time you

Given two words word1 and word2, find the minimum number of steps required to convert word1 to word2. (each operation is counted as 1 step.) You have the following 3 operations permitted on a word:

The string "PAYPALISHIRING" is written in a zigzag 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 N A P L S I

Given an array of strings, return all groups of strings that are anagrams. Note: All inputs will be in lower-case. public class Solution { public List anagrams(String[] strs) { HashM

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. The brackets must close in the correct order, "()" and "()[]{}" are all va

Given an unsorted integer array, find the first missing positive integer. For example, Given [1,2,0] return 3, and [3,4,-1,1] return 2. Your algorithm should run in O(n) time and uses constant

Given an array of integers, find two numbers such that they add up to a specific target number. The function twoSum should return indices of the two numbers such that they add up to the target, whe

The count-and-say sequence is the sequence of integers beginning as follows: 1, 11, 21, 1211, 111221, ... 1 is read off as "one 1" or 11. 11 is read off as "two 1s" or 21. 21 is read off as 

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time. push(x) -- Push element x onto stack.pop() -- Removes the element on top of the stack.top() -- Get

Given n, generate all structurally unique BST's (binary search trees) that store values 1...n. For example, Given n = 3, your program should return all 5 unique BST's shown below. public class

public class Solution { public List> threeSum(int[] num) { ArrayList> result=new ArrayList>(); int len=num.length; if(len==0)return result; Arrays.sort(num);

Trapping rain water的最naive的方法：onepass 没有注意到的问题： 1一个container的两端应该是取最小的高度。 2在找第一个容器的左端的时候没有注意到数组的下标的界限的问题！注意当数组的下标有变化的时候一定紧跟着不要忘记对其范围进行限制。 3解题思路是：先找到第一个容器的最左端的点，然后用一个函数去找这个容器的右端，这个右端或者是大于等于这个容器的左端，

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: "((()))", "(()())", "(())()", "()(())", "()()

Given a collection of numbers, return all possible permutations. For example, [1,2,3] have the following permutations: [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1]. public class

题目：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. You may assume that each input would have exac

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a link

Given two binary strings, return their sum (also a binary string). For example, a = "11" b = "1" Return "100". public class Solution { public String addBinary(String a, String b) {

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. Note: Element

Given a digit string, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telephone buttons) is given below. Input:Digit st

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. An example is the root-to-leaf path 1->2->3 which represents the number 123. Find the tota

Given a binary tree, determine if it is a valid binary search tree (BST). Assume a BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key.Th

Given a binary tree, find the maximum path sum. The path may start and end at any node in the tree. For example: Given the below binary tree, public class Solution { int result=Integer.M

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place. public class Solution { public void setZeroes(int[][] matrix) { int[] row=new int[matrix.le