Flip Game You are playing the following Flip Game with your friend: Given a string that contains only these two characters: + and -, you and your friend take turns to flip two consecutive”++” into “–“. The game ends when a person can no longer make a move and therefore […]
You are playing the following Nim Game with your friend: There is a heap of stones on the table, each time one of you take turns to remove 1 to 3 stones. The one who removes the last stone will be the winner. You will take the first turn to […]
Count Univalue Subtrees Given a binary tree, count the number of uni-value subtrees. A Uni-value subtree means all nodes of the subtree have the same value. For example: Given binary tree, 5 / \ 1 5 / \ \ 5 5 5 return 4. /** * Definition for a binary […]
Meeting Rooms Given an array of meeting time intervals consisting of start and end times [[s1,e1],[s2,e2],…] (si < ei), determine if a person could attend all meetings. For example, Given [[0, 30],[5, 10],[15, 20]], return false. Meeting Rooms II Given an array of meeting time intervals consisting of start […]
Count Primes Description: Count the number of prime numbers less than a non-negative number, n. Credits: Special thanks to @mithmatt for adding this problem and creating all test cases. A naive approach, check each i smaller than n that is prime or not. O(n^2), time limit exceeded. class Solution { […]
Valid Anagram Given two strings s and t, write a function to determine if t is an anagram of s. For example, s = “anagram”, t = “nagaram”, return true. s = “rat”, t = “car”, return false. Note: You may assume the string contains only lowercase alphabets. use sort […]
Given a pattern and a string str, find if str follows the same pattern. Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in str. Examples: pattern = “abba”, str = “dog cat cat dog” should return true. […]
Expression Tree Build The structure of Expression Tree is a binary tree to evaluate certain expressions. All leaves of the Expression Tree have an number string value. All non-leaves of the Expression Tree have an operator string value. Now, given an expression array, build the expression tree of this expression, […]
Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times. The algorithm should run in linear time and in O(1) space. Hint: How many majority elements could it possibly have? Do you have a better hint? Suggest it! Vote for the majority. […]
Shortest Palindrome Given a string S, you are allowed to convert it to a palindrome by adding characters in front of it. Find and return the shortest palindrome you can find by performing this transformation. For example: Given “aacecaaa”, return “aaacecaaa”. Given “abcd”, return “dcbabcd”. Credits: Special thanks to @ifanchu […]