A robot is located at the top-left corner of a m x n grid. It can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid. How many possible unique paths are there? Java Solution 1 – DFS A depth-first search solution … Read more
Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path. Java Solution 1: Depth-First Search A native solution would be depth-first search. It’s time is too expensive and fails the online judgement. public int minPathSum(int[][] grid) … Read more
Given an array of n positive integers and a positive integer s, find the minimal length of a subarray of which the sum ≥ s. If there isn’t one, return 0 instead. For example, given the array [2,3,1,2,4,3] and s = 7, the subarray [4,3] has the minimal length of 2 under the problem constraint. … Read more
Follow up for H-Index: What if the citations array is sorted in ascending order? Could you optimize your algorithm? Java Solution Given the array is sorted, we should use binary search. int hIndex(int[] citations) { int len = citations.length; if (len == 0) { return 0; } if (len == 1) { if … Read more
Implement a basic calculator to evaluate a simple expression string. The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should truncate toward zero. You may assume that the given expression is always valid. Some examples: “3+2*2” = 7 Java Solution public int calculate(String s) { … Read more
5/10/2016 1. Add about 20 more problems. 2. Optimize solutions for some old problems. 5/17/2016 1. Add 12 more problems. 2. Optimize solutions for some old problems. 3. Remove some naive solutions because they are too obvious and have no values. 8/1/2016 1. Add 30 more problems. 2. Optimize solutions for some old problems. 3. … Read more
Write a program to find the n-th ugly number. Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers. Note that 1 is typically treated as an ugly number. Java Solution … Read more
Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 – 1. For example, 123 -> “One Hundred Twenty Three” 12345 -> “Twelve Thousand Three Hundred Forty Five” Java Solution This problem is straightforward, but the corner cases should be considered carefully. public class Solution { HashMap<Integer, … Read more
Given an input string, reverse the string word by word. A word is defined as a sequence of non-space characters. The input string does not contain leading or trailing spaces and the words are always separated by a single space. For example, Given s = “the sky is blue”, return “blue is sky the”. Could … Read more
Write a program to check whether a given number is an ugly number. Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not ugly since it includes another prime factor 7. Note that 1 is typically treated as an ugly number. Java … Read more
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 fence. Java Solution The key to solve … Read more
There are n bulbs that are initially off. You first turn on all the bulbs. Then, you turn off every second bulb. On the third round, you toggle every third bulb (turning on if it’s off or turning off if it’s on). For the ith round, you toggle every i bulb. For the nth round, … Read more
You are a product manager and currently leading a team to develop a new product. Unfortunately, the latest version of your product fails the quality check. Since each version is developed based on the previous version, all the versions after a bad version are also bad. Suppose you have n versions [1, 2, …, n] … Read more
Given two strings s1 and s2 of the same length, determine if s2 is a scrambled string of s1. Java Solution public boolean isScramble(String s1, String s2) { if(s1.length()!=s2.length()) return false; if(s1.length()==0 || s1.equals(s2)) return true; char[] arr1 = s1.toCharArray(); char[] arr2 = s2.toCharArray(); Arrays.sort(arr1); Arrays.sort(arr2); if(!new String(arr1).equals(new String(arr2))){ return false; } … Read more
Given two strings S and T, determine if they are both one edit distance apart. Java Solution public boolean isOneEditDistance(String s, String t) { if(s==null || t==null) return false; int m = s.length(); int n = t.length(); if(Math.abs(m-n)>1){ return false; } int i=0; int j=0; int count=0; while(i<m&&j<n){ if(s.charAt(i)==t.charAt(j)){ i++; j++; … Read more