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 { […]