喜欢反对

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 "o

Idea: the regular approach is to us split method in Java    that split each word by space " ", then reverse each word from back to front.    Watch out for the special cases.    remember to elimi

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.Have y

Given an index k, return the kth row of the Pascal's triangle.For example, given k = 3,Return [1,3,3,1].Note:Could you optimize your algorithm to use only O(k) extra space?

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.For example,Given the following matrix:[ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ]]You

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]]Have you

Search a 2D Matrix :Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:Integers in each row are sorted from left to right.The

Write a function to find the longest common prefix string among st an array of strings.

/*Key to solve: * A Valid Parentheses pair contain only one left and right bracket. * 1. store index of '(' in the stack * 2. check stack whether is empty when ')' was found: * two case as

public class Solution { public String minWindow(String S, String T) { String output=""; if(S.length()==0 || T.length()==0) return ""; HashMap map=new HashMap(); int matchCount=0;

Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. Fo

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 ArrayList anagrams(String[] st

public class Solution { public ArrayList findSubstring(String S, String[] L) { ArrayList result=new ArrayList(); if(S.length()==0 || L.length==0) return result; HashMap m

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?Have you been asked this question in an i

public static int minCut(String s) { if(s==null || s.length()==0) return -1; int len=s.length(); boolean[][] dict=palinDict(s); int[] res=new int[len+1]; res[0]

Idea: Recursive-loop + dynamic programming + backtracking    Combination of Longest Palindromic Substring & Word Break II    There are two major steps:    1.palindromic dictionary that using sam

Two Approach: NP-problem    Solution#1: brute force of Recursive-loop, The appraoch is pretty    similar with N-Queens problem    Maintain a result List, traverse all the sub-String list    Ca

sadspublic class Solution { public String addBinary(String a, String b) { if(a.length()==0) return b; if(b.length()==0) return a; StringBuilder strBuilder=new StringBui

Idea: Dynamic programming + Nested Loop    outer loop: i start from 0 to N    inner loop: j start from 0 to i    Use a boolean array in size of N to record the previous info    res[i+1] pu

public class Solution { public int longestConsecutive(int[] num) { if(num.length==0) return 0; int maxCount=0; HashSet set=new HashSet(); //initial the HashSet wit

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).You are given a target value to search. If found in the array return it

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)).Key to solve: Bisection + Recur

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

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.

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.click to show follow up.Follow up:Did you use extra space?A straight forward solution using O(m

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,

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

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:Elements in a triplet (a,b,c

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:Elements

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, where

Solution: Time O(n^2)    same idea as 3 Sum    find minimum difference: abs(sum-target)

Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue.Here, we will use the integers

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

Goal: find Length of Last Word    the length will depend on the index of last Character - last index of  spacepublic class Solution { public int lengthOfLastWord(String s) { if(s.leng

Implement strStr().Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack. Goal: Determine whether needle is substring of haystack or not &

Idea: Nested loop:    Outer loop: i start from back to front    inner loop: j start from i to the endStated more formally below:Define P[i][j] ← true iffthe substring Si … Sj is a palindrome