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Validate if a given string is numeric.Some examples:"0" => true" 0.1 " => true"abc" => false public boolean isNumber(String s) { int i = 0, n = s.length(); boolean isNumeric = false;

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 3...

In the "100 game," two players take turns adding, to a running total, any integer from 1..10. The player who first causes the running total to reach or exceed 100 wins.What if we change the game so

Given two sparse matrices A and B, return the result of AB.You may assume that A's column number is equal to B's row number.Example:A = [ [ 1, 0, 0], [-1, 0, 3]]B = [ [ 7, 0, 0 ],

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

Given a set ofnon-overlappingintervals, insert a new interval into the intervals (merge if necessary).You may assume that the intervals were initially sorted according to their start times.Examp...

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 house

This is a follow up of Shortest Word Distance. The only difference is now you are given the list of words and your method will be called repeatedly many times with different parameters. How would yo

Given a list of words and two words word1 and word2, return the shortest distance between these two words in the list.For example,Assume that words = ["practice", "makes", "perfect", "coding", "

Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be...

Suppose you have a long flowerbed in which some of the plots are planted and some are not. However, flowers cannot be planted in adjacent plots - they would compete for water and both would die.Gi

Design and implement a TwoSum class. It should support the following operations: add and find.add - Add the number to an internal data structure.find - Find if there exists any pair of numbers w

Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord, such that:Only one letter can be changed at a

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two node

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:

Given an integer, convert it to a roman numeral.Input is guaranteed to be within the range from 1 to 3999.要点就是要把900,400等特殊数字的表达方式加上，再按大小依次往下除即可 public String intToRoman(int num) { if(num &...

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 larges

Given a string S and a string T, find the minimum window in S which will contain all the characters in T in complexity O(n).For example,S = "ADOBECODEBANC"T = "ABC"Minimum window is "BANC".

You need to find the largest value in each row of a binary tree.Example:Input: 1 / \ 3 2 / \ \ 5 3 9 Output: [1, 3, 9]/** * Definition f

Given a collection of intervals, merge all overlapping intervals.For example,Given [1,3],[2,6],[8,10],[15,18],return [1,6],[8,10],[15,18].public class Solution { public List merge(

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and put.get(key) - Get the value (will always be positive) of the key i

Given a nested list of integers, return the sum of all integers in the list weighted by their depth.Each element is either an integer, or a list -- whose elements may also be integers or other lis

Implement pow(x, n).public class Solution { public double myPow(double x, int n) { if(n >= 0){ return pow(x, n); } return 1/pow(x, -n); }

Given two strings s and t, determine if they are isomorphic.Two strings are isomorphic if the characters in s can be replaced to get t.All occurrences of a character must be replaced with anot

Numbers can be regarded as product of its factors. For example,8 = 2 x 2 x 2; = 2 x 4.Write a function that takes an integer n and return all possible combinations of its factors.Note: 

There are a row of n houses, each house can be painted with one of the three colors: red, blue or green. The cost of painting each house with a certain color is different. You have to paint all the ho

Given a binary tree where all the right nodes are either leaf nodes with a sibling (a left node that shares the same parent node) or empty, flip it upside down and turn it into a tree where the origin

Given a nested list of integers, return the sum of all integers in the list weighted by their depth.Each element is either an integer, or a list -- whose elements may also be integers or other lis

This is a follow up of Shortest Word Distance. The only difference is now word1 could be the same as word2.Given a list of words and two words word1 and word2, return the shortest distance betwe

Given a positive integer num, write a function which returns True if num is a perfect square else False.Note: Do not use any built-in library function such as sqrt.Example 1:Input: 16Returns: T

Given a binary tree, collect a tree's nodes as if you were doing this: Collect and remove all leaves, repeat until the tree is empty.Example:Given binary tree  1 / \

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] ha

Suppose you are at a party with n people (labeled from 0 to n - 1) and among them, there may exist one celebrity. The definition of a celebrity is that all the other n - 1 people know him/her but

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.public class Solution { public int maxPoints(Point[] points) { if (points == nul

Given a collection of distinct 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], [3,2,1

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.Calling next() will return the next smallest number in the BST.Note: next() a

Given a collection of numbers that might contain duplicates, return all possible unique permutations.For example,[1,1,2] have the following unique permutations:[ [1,1,2], [1,2,1], [2,1

Given an array of integers sorted in ascending order, find the starting and ending position of a given target value.Your algorithm's runtime complexity must be in the order of O(log n).If the

All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T, for example: "ACGAATTCCG". When studying DNA, it is sometimes useful to identify repeated sequences within the DNA.Write

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