Given a digit string, return all possible letter combinations that the number could represent. (Check out your cellphone to see the mappings) Input:Digit string “23”, Output: [“ad”, “ae”, “af”, “bd”, “be”, “bf”, “cd”, “ce”, “cf”]. Java Solution 1 – DFS This problem can be solves by a typical DFS algorithm. DFS problems are very similar … Read more
Write an algorithm to determine if a number is “happy”. What is an happy number can be shown in the following example: 19 is a happy number 1^2 + 9^2 = 82 8^2 + 2^2 = 68 6^2 + 8^2 = 100 1^2 + 0^2 + 0^2 = 1 Analysis The key to solve this … Read more
Remove all elements from a linked list of integers that have value val. Example Given: 1 –> 2 –> 6 –> 3 –> 4 –> 5 –> 6, val = 6 Return: 1 –> 2 –> 3 –> 4 –> 5 Java Solution The key to solve this problem is using a helper node to … Read more
Given a 2D board containing ‘X’ and ‘O’, capture all regions surrounded by ‘X’. A region is captured by flipping all ‘O’s into ‘X’s in that surrounded region. For example, X X X X X O O X X X O X X O X X After running your function, the board should be: X … Read more
Given an index k, return the kth row of the Pascal’s triangle. For example, when k = 3, the row is [1,3,3,1]. Analysis This problem is related to Pascal’s Triangle which gets all rows of Pascal’s triangle. In this problem, only one row is required to return. Java Solution public List<Integer> getRow(int rowIndex) { ArrayList<Integer> … Read more
Given a string s, partition s such that every substring of the partition is a palindrome. Return the minimum cuts needed for a palindrome partitioning of s. For example, given s = “aab”, return 1 since the palindrome partitioning [“aa”,”b”] could be produced using 1 cut. Analysis This problem is similar to Palindrome Partitioning. It … Read more
Given a range [m, n] where 0
Given n points on a 2D plane, find the maximum number of points that lie on the same straight line. Analysis This problem can be solve by counting points that have the same slope for each point. When counting, we need to be careful about the duplicate points and points on the vertical lines. Java … Read more
Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. For example, consider the following matrix: [ [1, 4, 7, … Read more
Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom. For example, given the following binary tree, 1
Given a 2-d grid map of ‘1’s (land) and ‘0’s (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: 11110 11010 11000 00000 Answer: 1 Java … Read more
Given an unsorted array of integers, find the length of longest increasing subsequence. For example, given [10, 9, 2, 5, 3, 7, 101, 18], the longest increasing subsequence is [2, 3, 7, 101]. Therefore the length is 4. Java Solution 1 – Naive Let max[i] represent the length of the longest increasing subsequence so far. … Read more
The longest common subsequence (LCS) problem is the problem of finding the longest subsequence common to all sequences in a set of sequences (often just two sequences). Analysis Let dp[i+1][j+1] be the length of the longest common subsequence of string a & b, when a[i] and b[j] are compared to each other. (0
Given an integer, write a function to determine if it is a power of three. Java Solution 1 – Iteration public boolean isPowerOfThree(int n) { if(n==1) return true; boolean result = false; while(n>0){ int m = n%3; if(m==0){ n=n/3; if(n==1) return true; }else{ return false; } } return result; }public boolean isPowerOfThree(int … Read more
Given an integer n, return the number of trailing zeroes in n!. Note: Your solution should be in logarithmic time complexity. Java Solution public int trailingZeroes(int n) { if (n < 0) return -1; int count = 0; for (long i = 5; n / i >= 1; i *= 5) { count += … Read more