Given an array and a value, remove all instances of that value in place and return the new length. (Note: The order of elements can be changed. It doesn’t matter what you leave beyond the new length.) Java Solution This problem can be solve by using two indices. public int removeElement(int[] A, int elem) { … Read more
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
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 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
Problem Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST. Calling next() will return the next smallest number in the BST. Note: next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree. … Read more
Example: -2 (K) -3 3 -5 -10 1 10 30 -5 (P) Java Solution This problem can be solved by using dynamic programming. We maintain a 2-D table. h[i][j] is the minimum health value before he enters (i,j). h[0][0] is the value of the answer. The left part is filling in numbers to the table. … Read more
You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses have security system connected and it will automatically contact the police if two adjacent houses were broken into on the … Read more