Given a non-negative number represented as a singly linked list of digits, plus one to the number. The digits are stored such that the most significant digit is at the head of the list. Example: Input: 1->2->3 Output: 1->2->4 Java Solution public ListNode plusOne(ListNode head) { ListNode h2 = reverse(head); ListNode p=h2; while(p!=null){ … Read more
Design a Phone Directory which supports the following operations: get: Provide a number which is not assigned to anyone. check: Check if a number is available or not. release: Recycle or release a number. Java Solution 1 public class PhoneDirectory { int max; HashSet<Integer> set; LinkedList<Integer> queue; /** Initialize your data structure here @param … Read more
Shuffle a set of numbers without duplicates. Java Solution How we make sure each the probability of each element get shuffled is very similar to the streaming random problem. The algorithm is straightforward to understand, but the question is why it works. To have a working shuffle algorithm, every element in the array results in … Read more
Given a nested list of integers represented as a string, implement a parser to deserialize it. Each element is either an integer, or a list — whose elements may also be integers or other lists. Note: You may assume that the string is well-formed: String is non-empty. String does not contain white spaces. String contains … Read more
Given a non-empty 2D matrix matrix and an integer k, find the max sum of a rectangle in the matrix such that its sum is no larger than k. Example: Given matrix = [ [1, 0, 1], [0, -2, 3] ] k = 2 The answer is 2. Because the sum of rectangle [[0, 1], … Read more
Given a set of distinct positive integers, find the largest subset such that every pair (Si, Sj) of elements in this subset satisfies: Si % Sj = 0 or Sj % Si = 0. If there are multiple solutions, return any subset is fine. Example 1: nums: [1,2,3] Result: [1,2] (of course, [1,3] will also … Read more
Given a singly linked list, return a random node’s value from the linked list. Each node must have the same probability of being chosen. Follow up: What if the linked list is extremely large and its length is unknown to you? Could you solve this efficiently without using extra space? Java Solution This problem is … Read more
Design a data structure that supports all following operations in average O(1) time. Note: Duplicate elements are allowed. insert(val): Inserts an item val to the collection. remove(val): Removes an item val from the collection if present. getRandom(): Returns a random element from current collection of elements. The probability of each element being returned is linearly … Read more
Design a data structure that supports all following operations in O(1) time. insert(val): Inserts an item val to the set if not already present. remove(val): Removes an item val from the set if present. getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned. Java … Read more
Given a data stream input of non-negative integers a1, a2, …, an, …, summarize the numbers seen so far as a list of disjoint intervals. For example, suppose the integers from the data stream are 1, 3, 7, 2, 6, …, then the summary will be: [1, 1] [1, 1], [3, 3] [1, 1], [3, … Read more
This is a follow-up problem of Shortest Word Distance. The only difference is now word1 could be the same as word2. Given a list of words and two words word1 and word2, return the shortest distance between these two words in the list. word1 and word2 may be the same and they represent two individual … Read more
Given a list of words and two words word1 and word2, return the shortest distance between these two words in the list. For example, Assume that words = [“practice”, “makes”, “perfect”, “coding”, “makes”]. Given word1 = “codingâ€, word2 = “practiceâ€, return 3. Given word1 = “makes”, word2 = “coding”, return 1. Java Solution public int … Read more
For a undirected graph with tree characteristics, we can choose any node as the root. The result graph is then a rooted tree. Among all possible rooted trees, those with minimum height are called minimum height trees (MHTs). Given such a graph, write a function to find all the MHTs and return a list of … Read more
Given a binary tree, find the largest subtree which is a Binary Search Tree (BST), where largest means subtree with largest number of nodes in it. Java Solution class Wrapper{ int size; int lower, upper; boolean isBST; public Wrapper(){ lower = Integer.MAX_VALUE; upper = Integer.MIN_VALUE; isBST = false; size = 0; } } public … Read more
Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target. Java Solution This problem is similar to Coin Change. It’s a typical dynamic programming problem. public int combinationSum4(int[] nums, int target) { if(nums==null || nums.length==0) return 0; int[] dp … Read more