Given a set of distinct integers, S, return all possible subsets. Note: Elements in a subset must be in non-descending order. The solution set must not contain duplicate subsets. For example, If S = [1,2,3], a solution is: [ [3], [1], [2], [1,2,3], [1,3], [2,3], [1,2], [] ] Thoughts Comparing this problem with Subsets can … Read more
Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length. Do not allocate extra space for another array, you must do this in place with constant memory. For example, given input array A = [1,1,2], your function should return length = 2, and A … Read more
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 [1,1,2,2,3]. So this problem also requires in-place array manipulation. Java Solution 1 We can not change the given array’s size, so we only … Read more
Given an array where elements are sorted in ascending order, convert it to a height balanced BST. Java Solution A typical DFS problem using recursion. // Definition for binary tree class TreeNode { int val; TreeNode left; TreeNode right; TreeNode(int x) { val = x; } } public class Solution { public TreeNode … Read more
Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST. Thoughts If you are given an array, the problem is quite straightforward. But things get a little more complicated when you have a singly linked list instead of an array. Now you no longer have random … Read more
Given a string S and a string T, count the number of distinct subsequences of T in S. A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (ie, “ACE” is … Read more
Given a set of distinct integers, S, return all possible subsets. Note: 1) Elements in a subset must be in non-descending order. 2) The solution set must not contain duplicate subsets. For example, given S = [1,2,3], the method returns: [ [3], [1], [2], [1,2,3], [1,3], [2,3], [1,2], [] ] Thoughts Given a set S … Read more
Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below. For example, given the following triangle [ [2], [3,4], [6,5,7], [4,1,8,3] ] The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = … Read more
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? In-place Solution By using the relation “matrix[i][j] = matrix[n-1-j][i]”, we can loop through the matrix. public void rotate(int[][] matrix) { int n = matrix.length; for (int i = 0; … Read more
Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has properties: 1) Integers in each row are sorted from left to right. 2) The first integer of each row is greater than the last integer of the previous row. For example, consider the following matrix: [ [1, … Read more
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 should return [1,2,3,6,9,8,7,4,5]. Java Solution 1 If more than one … Read more
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example, “Red rum, sir, is murder” is a palindrome, while “Programcreek is awesome” is not. Note: Have you consider that the string might be empty? This is a good question to ask during an interview. For the purpose … Read more
Given an unsorted array of integers, find the length of the longest consecutive elements sequence. For example, given [100, 4, 200, 1, 3, 2], the longest consecutive elements sequence should be [1, 2, 3, 4]. Its length is 4. Your algorithm should run in O(n) complexity. Java Solution 1 Because it requires O(n) complexity, we … Read more
Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order. You may assume no duplicates in the array. Here are few examples. [1,3,5,6], 5 -> 2 [1,3,5,6], 2 -> 1 [1,3,5,6], 7 -> 4 … Read more
Given inorder and postorder traversal of a tree, construct the binary tree. Analysis This problem can be illustrated by using a simple example. in-order: 4 2 5 (1) 6 7 3 8 post-order: 4 5 2 6 7 8 3 (1) From the post-order array, we know that last element is the root. We can … Read more