Find the contiguous subarray within an array (containing at least one number) which has the largest sum.For example, given the array [−2,1,−3,4,−1,2,1,−5,4], the contiguous subarray [4,−1,2,1] has the

There are n coins in a line. (Assume n is even). Two players take turns to take a coin from one of the ends of the line until there are no more coins left. The player with the larger amount of money w

[code]public class Solution { public int romanToInt(String s) { if(s==null || s.length()==0)return 0; int r=0,i=0; while(i<s.length()) { if(s.charAt(i)==

Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length.Do not allocate extra space for another array, you must do this in place with cons

除了1个元素出现一次之外其他均出现2次，用exclusive or (^).general case: public class Solution { public int singleNumber(int[] A) { if (A == null) return 0; int x0 = ~0, x1 = 0, x2 = 0, t; for

[code]public class Solution { public List<Integer> spiralOrder(int[][] matrix) { trace=new ArrayList<Integer>(); if(matrix==null || matrix.length==0 || matrix[0].length==0)return tr

[code]public class Solution { int dp[][]; public int uniquePathsWithObstacles(int[][] obstacleGrid) { if( obstacleGrid==null || obstacleGrid.length==0 )return 0; int m=obstacleG

Find the contiguous subarray within an array (containing at least one number) which has the largest product.For example, given the array [2,3,-2,4], the contiguous subarray [2,3] has the largest produ

[code]/** * Definition for undirected graph. * class UndirectedGraphNode { * int label; * List<UndirectedGraphNode> neighbors; * UndirectedGraphNode(int x) { label = x; neighbors = new

[code]public class Solution { public boolean isValid(String s) { if(s==null || s.length()==0)return true; Stack<Character> stack=new Stack<Character>(); HashMap <Character,

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.[code]public class S

[code]public class Solution { public String intToRoman(int num) { StringBuffer sb=new StringBuffer(); int t=num/1000; num%=1000; for(int i=0;i<t;i++)sb.append('M');

[code]public class Solution { public int evalRPN(String[] tokens) { if( tokens==null || tokens.length==0 )return 0; Stack<Integer> stack=new Stack<Integer>(); int i=0;

Given a sorted linked list, delete all duplicates such that each element appear only once.For example, Given 1->1->2, return 1->2. Given 1->1->2->3->3, return 1->2->3.**[code]**Remove Duplicates from

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.For example, Given 1->2->3->3->4->4->5, return 1->2->5. Given 1->1->1->2

[code]class MinStack { ArrayList<Integer> stack=new ArrayList<Integer>(); ArrayList<Integer> mins=new ArrayList<Integer>(); public void push(int x) { stack.add(x); if(mins.i

Given 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 the array.Here

Follow up for “Remove Duplicates”: What if duplicates are allowed at most twice?For example, Given sorted array A = [1,1,1,2,2,3],Your function should return length = 5, and A is now [1,1,2,2,3].[cod

There are two sorted arrays A and B 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)).[code]public class Solution { publ

Implement 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 lowest possible orde

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.For example, Given [100, 4, 200, 1, 3, 2], The longest consecutive elements sequence is [1, 2, 3, 4].

Two SumGiven 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, w

Given an array and a value, remove all instances of that value in place and return the new length.The order of elements can be changed. It doesn’t matter what you leave beyond the new length.[code]publ

Given a linked list, swap every two adjacent nodes and return its head. For example, Given 1->2->3->4, you should return the list as 2->1->4->3.Your algorithm should use only constant space. You

Given a linked list, remove the nth node from the end of list and return its head. For example, Given linked list: 1->2->3->4->5, and n = 2. After removing the second node from the end, the linke

The gray code is a binary numeral system where two successive values differ in only one bit.Given a non-negative integer n representing the total number of bits in the code, print the sequence of gray

[code] Memory limit exceededpublic class Solution { public ListNode partition(ListNode head, int x) { if(head ==null || head.next==null)return head; ListNode d1=new ListNode(0), d2

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) { if(matrix==null)return;

Given a list, rotate the list to the right by k places, where k is non-negative.For example: Given 1->2->3->4->5->NULL and k = 2, return 4->5->1->2->3->NULL.[code]public class Solution { public L

Valid sudokuDetermine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules. The Sudoku board could be partially filled, where empty cells are filled with the character ‘.’.public class Solut

Given 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. For example, Given [0,1,0,2,1,0,1,3,2,1,2,1]

You are given an n x n 2D matrix representing an image. Rotate the image by 90 degrees (clockwise). Follow up: Could you do this in-place?[code]public class Solution { public void rotate(int[][]

Reverse a linked list from position m to n. Do it in-place and in one-pass For example: Given 1->2->3->4->5->NULL, m = 2 and n = 4, return 1->4->3->2->5->NULL.Note: Given m, n satisfy the fol

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 linke

N-Queens IThe 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 puz

Given a string s consists of upper/lower-case alphabets and empty space characters ’ ‘, return the length of last word in the string. If the last word does not exist, return 0. Note: A word is define

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

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path. Note: You can only move either down or right at an

You are climbing a stair case. It takes n steps to reach to the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?public class Solution { public

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.Return a deep copy of the list.[code]/** * Definition for singly-link