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
Given a sequence of integers, return the length of the longest subsequence that is a wiggle sequence. A subsequence is obtained by deleting some number of elements (eventually, also zero) from the original sequence, leaving the remaining elements in their original order. Java Solution The problem is converted to finding the turning point. When nums[i] … Read more
Numbers can be regarded as product of its factors. For example, 8 = 2 x 2 x 2; = 2 x 4. Write a function that takes an integer n and return all possible combinations of its factors. Note: You may assume that n is always positive. Factors should be greater than 1 and less … Read more
Given a binary tree, collect a tree’s nodes as if you were doing this: Collect and remove all leaves, repeat until the tree is empty. Example: Given binary tree 1 / \ 2 3 / \ 4 5 Returns [4, 5, 3], [2], [1]. Java Solution 1 Naively, we can get the order of each … Read more
This is the extension problem of Word Pattern I. 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 substring in str. Examples: pattern = “abab”, str = “redblueredblue” should return … Read more
Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i]. Solve it without division and in O(n). For example, given [1,2,3,4], return [24,12,8,6]. Java Solution 1 public int[] productExceptSelf(int[] nums) { int[] result = … Read more
Write a function to delete a node (except the tail) in a singly linked list, given only access to that node. Supposed the linked list is 1 -> 2 -> 3 -> 4 and you are given the third node with value 3, the linked list should become 1 -> 2 -> 4 after calling … Read more
There following Java code shows how to implement a queue without using any extra data structures in Java. We can implement a queue by using an array. import java.lang.reflect.Array; import java.util.Arrays; public class Queue<E> { E[] arr; int head = -1; int tail = -1; int size; public Queue(Class<E> c, int size) … Read more
Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree. Java Solution 1 public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { if(root==null) return null; if(root==p || root==q) return root; TreeNode l = lowestCommonAncestor(root.left, p, q); TreeNode r = lowestCommonAncestor(root.right, p, q); if(l!=null&&r!=null){ return root; … Read more
Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST. Analysis This problem can be solved by using BST property, i.e., left < parent < right for each node. There are 3 cases to handle. Java Solution 1 – Recursive public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, … Read more