Given a linked list, swap every two adjacent nodes and return its head. For example, given 1->2->3->4, you should return the list as 2->1->4->3. Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed. Java Solution 1 Use two template variable to track … Read more
Count the number of prime numbers less than a non-negative number, n Java Solution 1 This solution exceeds time limit. public int countPrimes(int n) { n = n-1; ArrayList<Integer> primes = new ArrayList<Integer>(); if(n<=1) return 0; if(n==2) return 1; if(n==3) return 2; primes.add(2); primes.add(3); for(int i=4; i<=n; i++){ boolean isPrime = … Read more
Given a binary tree, find the length of the longest consecutive sequence path. The path refers to any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The longest consecutive path need to be from parent to child (cannot be the reverse). Java Solution 1 – BFS … Read more
Given an absolute path for a file (Unix-style), simplify it. For example, path = “/home/”, => “/home” path = “/a/./b/../../c/”, => “/c” path = “/../”, => “/” path = “/home//foo/”, => “/home/foo” Java Solution public String simplifyPath(String path) { Stack<String> stack = new Stack<String>(); //stack.push(path.substring(0,1)); while(path.length()> 0 && path.charAt(path.length()-1) ==’/’){ path = path.substring(0, … Read more
Given a string array words, find the maximum value of length(word[i]) * length(word[j]) where the two words do not share common letters. You may assume that each word will contain only lower case letters. If no such two words exist, return 0. Java Solution public int maxProduct(String[] words) { if(words==null || words.length==0) return 0; … Read more
Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive. The update(i, val) function modifies nums by updating the element at index i to val. Java Solution 1 – Segment Tree class TreeNode{ int start; int end; int sum; TreeNode leftChild; TreeNode rightChild; public … Read more
Given a sorted array of integers, find the starting and ending position of a given target value. Your algorithm’s runtime complexity must be in the order of O(log n). If the target is not found in the array, return [-1, -1]. For example, given [5, 7, 7, 8, 8, 10] and target value 8, return … Read more
Given an array of strings, return all groups of strings that are anagrams. An anagram is a type of word play, the result of rearranging the letters of a word or phrase to produce a new word or phrase, using all the original letters exactly once; for example, Torchwood can be rearranged into Doctor Who. … Read more
Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by its upper left corner (row1, col1) and lower right corner (row2, col2). Analysis Since the assumption is that there are many calls to sumRegion method, we should use some extra space to store the intermediate results. The solution is … Read more
Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T. Each number in C may only be used ONCE in the combination. Note: 1) All numbers (including target) will be positive integers. 2) Elements in a combination (a1, a2, … … Read more
Given a binary tree, return the bottom-up level order traversal of its nodes’ values. For example, given binary tree {3,9,20,#,#,15,7}, 3 / \ 9 20 / \ 15 7 return its level order traversal as [[15,7], [9,20],[3]] Java Solution public List<ArrayList<Integer>> levelOrderBottom(TreeNode root) { ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>(); if(root == null){ return result; … Read more
Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level). For example: Given binary tree {3,9,20,#,#,15,7}, 3 / \ 9 20 / \ 15 7 return its level order traversal as [[3], [9,20], [15,7]] Java Solution 1 It is obvious that this problem can … Read more
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