ProgramCreek Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher’s h-index. A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each. For example, … Read more
You are playing the following Bulls and Cows game with your friend: You write down a number and ask your friend to guess what the number is. Each time your friend makes a guess, you provide a hint that indicates how many digits in said guess match your secret number exactly in both digit and … Read more
Implement a trie with insert, search, and startsWith methods. Java Solution 1 A trie node should contains the character, its children and the flag that marks if it is a leaf node. You can use the trie in the following diagram to walk though the Java solution. class TrieNode { char c; HashMap<Character, TrieNode> children … Read more
Given an array containing n distinct numbers taken from 0, 1, 2, …, n, find the one that is missing from the array. For example, given nums = [0, 1, 3] return 2. Java Solution 1 – Math public int missingNumber(int[] nums) { int sum=0; for(int i=0; i<nums.length; i++){ sum+=nums[i]; } int n=nums.length; return … Read more
Java Solution This problem can be solved by BFS. We define one matrix for tracking the distance from each building, and another matrix for tracking the number of buildings which can be reached. public int shortestDistance(int[][] grid) { int[][] distance = new int[grid.length][grid[0].length]; int[][] reach = new int[grid.length][grid[0].length]; int numBuilding = 0; for … Read more
Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure. Java Solution Inorder traveral will return values in an increasing order. So if an element is less than its previous element,the previous element is a swapped node. public class Solution { TreeNode first; TreeNode second; TreeNode … Read more
Given n nodes labeled from 0 to n – 1 and a list of undirected edges (each edge is a pair of nodes), check if these edges form a valid tree. Analysis This problem can be converted to finding the cycle from a graph. It can be solved by using DFS (Recursion) or BFS (Queue). … Read more
Given a binary tree, find its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. Java Solution public int maxDepth(TreeNode root) { if(root==null) return 0; int leftDepth = maxDepth(root.left); int rightDepth = maxDepth(root.right); int bigger = Math.max(leftDepth, rightDepth); … Read more
Given a binary tree, return all root-to-leaf paths. 1. Naive DFS Solution A typical depth-first search problem. public List<String> binaryTreePaths(TreeNode root) { ArrayList<String> finalResult = new ArrayList<String>(); if(root==null) return finalResult; ArrayList<String> curr = new ArrayList<String>(); ArrayList<ArrayList<String>> results = new ArrayList<ArrayList<String>>(); dfs(root, results, curr); for(ArrayList<String> al : results){ StringBuilder sb = new … Read more
Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target. Java Solution 1 – Recursion Recursively traverse down the root. When target is less than root, go left; when target is greater than root, go right. public class Solution { int goal; double … Read more
Given a pattern and a string str, find if str follows the same pattern. Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in str. Java Solution public boolean wordPattern(String pattern, String str) { String[] arr = str.split(" "); //prevent out of … Read more
Given a nested list of integers, implement an iterator to flatten it. Each element is either an integer, or a list — whose elements may also be integers or other lists. For example, given the list [[1,1],2,[1,1]], by calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1]. … Read more
Given an array of integers, write a method to return the k most frequent elements. Java Solution 1 – Heap Time complexity is O(n*log(k)). Note that heap is often used to reduce time complexity from n*log(n) (see solution 3) to n*log(k). public List<Integer> topKFrequent(int[] nums, int k) { //count the frequency for each element HashMap<Integer, … Read more
Given a string, we can “shift” each of its letter to its successive letter, for example: “abc” -> “bcd”. We can keep “shifting” which forms the sequence: “abc” -> “bcd” -> … -> “xyz”. Given a list of strings which contains only lowercase alphabets, group all strings that belong to the same shifting sequence, return: … Read more
Given two strings s and t, write a function to determine if t is an anagram of s. Java Solution 1 Assuming the string contains only lowercase alphabets, here is a simple solution. public boolean isAnagram(String s, String t) { if(s==null || t==null) return false; if(s.length()!=t.length()) return false; int[] arr = new int[26]; … Read more