Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one. Note: You must not modify the array (assume the array is […]
H-Index Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher’s h-index. According to the definition of h-index on Wikipedia: “A scientist has index h if h of his/her N papers have at leasth citations each, and the other […]
Paint Fence There is a fence with n posts, each post can be painted with one of the k colors. You have to paint all the posts such that no more than two adjacent fence posts have the same color. Return the total number of ways you can paint the […]
Perfect Squares Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, …) which sum to n. For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 […]
Zigzag Iterator Given two 1d vectors, implement an iterator to return their elements alternately. For example, given two 1d vectors: v1 = [1, 2] v2 = [3, 4, 5, 6] By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1, 3, 2, […]
You are given a m x n 2D grid initialized with these three possible values. -1 – A wall or an obstacle. 0 – A gate. INF – Infinity means an empty room. We use the value 231 – 1 = 2147483647 to represent INF as you may assume that […]
Move Zeroes Given an array nums, write a function to move all 0‘s to the end of it while maintaining the relative order of the non-zero elements. For example, given nums = [0, 1, 0, 3, 12], after calling your function, nums should be [1, 3, 12, 0, 0]. Note: […]
Peeking Iterator Given an Iterator class interface with methods: next() and hasNext(), design and implement a PeekingIterator that support the peek() operation — it essentially peek() at the element that will be returned by the next call to next(). Here is an example. Assume that the iterator is initialized to […]
Generating maze is amazing! This algorithm is also widely used in lots of computer games. Given a 2D array, generate a maze in it. There are several requirements of this maze: There are no circles in the maze, which means all roads in the maze lead to an dead end or to […]
Inorder Successor in BST Given a binary search tree and a node in it, find the in-order successor of that node in the BST. Note: If the given node has no in-order successor in the tree, return null. o(h) time, o(1) space. If root->val > p->val, root is a possible […]
