Given an array of meeting time intervals consisting of start and end times [[s1,e1],[s2,e2],…] find the minimum number of conference rooms required. Java Solution When a room is taken, the room can not be used for anther meeting until the current meeting is over. As soon as the current meeting is finished, the room can … Read more
Follow up for “Unique Paths“: Now consider if some obstacles are added to the grids. How many unique paths would there be? An obstacle and empty space is marked as 1 and 0 respectively in the grid. For example, there is one obstacle in the middle of a 3×3 grid as illustrated below, [ [0,0,0], … Read more
Given an integer n, generate a square matrix filled with elements from 1 to n^2 in spiral order. For example, given n = 4, [ [1, 2, 3, 4], [12, 13, 14, 5], [11, 16, 15, 6], [10, 9, 8, 7] ] Java Solution 1 public int[][] generateMatrix(int n) { int total = n*n; int[][] … Read more
Given two numbers represented as strings, return multiplication of the numbers as a string. Analysis The key to solve this problem is multiplying each digit of the numbers at the corresponding positions and get the sum values at each position. That is how we do multiplication manually. Java Solution public String multiply(String num1, String num2) … Read more
Given an array nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Java Solution public int[] maxSlidingWindow(int[] nums, int k) { … Read more
Given two arrays, write a function to compute their intersection. Example: Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2, 2]. Java Solution 1 public int[] intersect(int[] nums1, int[] nums2) { HashMap<Integer, Integer> map = new HashMap<Integer, Integer>(); for(int i: nums1){ if(map.containsKey(i)){ map.put(i, map.get(i)+1); }else{ map.put(i, 1); } } ArrayList<Integer> … Read more
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”. Java Solution public String minWindow(String s, String t) { HashMap<Character, Integer> goal = new HashMap<>(); int goalSize = … Read more
Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. Find the total sum of all root-to-leaf numbers. For example, 1 / \ 2 3 The root-to-leaf path 1->2 represents the number 12. The root-to-leaf path 1->3 represents the number 13. Return the sum = 12 + 13 = … Read more
Given a binary search tree and a node in it, find the in-order successor of that node in the BST. // Definition for a binary tree node. public class TreeNode { int val; TreeNode left; TreeNode right; TreeNode(int x) { val = x; } }// Definition for a binary tree node. public class TreeNode { … Read more
Divide two integers without using multiplication, division and mod operator. If it is overflow, return MAX_INT. Analysis This problem can be solved based on the fact that any number can be converted to the format of the following: num=a_0*2^0+a_1*2^1+a_2*2^2+…+a_n*2^n The time complexity is O(logn). Java Solution public int divide(int dividend, int divisor) { //handle special … Read more
Design a Tic-tac-toe game that is played between two players on a n x n grid. Java Solution 1 – Naive We can simply check the row, column and the diagonals and see if there is a winner. public class TicTacToe { int[][] matrix; /** Initialize your data structure here. */ public TicTacToe(int … Read more
Given n, generate all structurally unique BST’s (binary search trees) that store values 1…n. For example, Given n = 3, your program should return all 5 unique BST’s shown below. 1 3 3 2 1 \ / / / \ \ 3 2 1 1 3 2 / / \ \ 2 1 2 3 … Read more
Given n, how many structurally unique BST’s (binary search trees) that store values 1…n? For example, Given n = 3, there are a total of 5 unique BST’s. 1 3 3 2 1 \ / / / \ \ 3 2 1 1 3 2 / / \ \ 2 1 2 3 Analysis Let … Read more
Java Solution 1 – DFS public void wallsAndGates(int[][] rooms) { if(rooms==null || rooms.length==0||rooms[0].length==0) return; int m = rooms.length; int n = rooms[0].length; boolean[][] visited = new boolean[m][n]; for(int i=0; i<m; i++){ for(int j=0; j<n; j++){ if(rooms[i][j]==0){ fill(rooms, i-1, j, 0, visited); fill(rooms, i, j+1, 0, visited); fill(rooms, i+1, j, 0, visited); fill(rooms, … Read more
Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Java Solution 1 – Level Order Traveral // … Read more