Given a sorted positive integer array nums and an integer n, add/patch elements to the array such that any number in range [1, n] inclusive can be formed by the sum of some elements in the array. Return the minimum number of patches required. Example 1: nums = [1, 3], n = 6 Return 1. … Read more
A 2d grid map of m rows and n columns is initially filled with water. We may perform an addLand operation which turns the water at position (row, col) into a land. Given a list of positions to operate, count the number of islands after each addLand operation. An island is surrounded by water and … Read more
Median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value. So the median is the mean of the two middle value. Analysis First of all, it seems that the best time complexity we can get for this problem is O(log(n)) of add() … Read more
One way to serialize a binary tree is to use pre-order traversal. When we encounter a non-null node, we record the node’s value. If it is a null node, we record using a sentinel value such as #. 9 / \ 3 2 / \ / \ 4 1 # 6 / \ / \ … Read more
Given an array nums and a target value k, find the maximum length of a subarray that sums to k. If there isn’t one, return 0 instead. Note: The sum of the entire nums array is guaranteed to fit within the 32-bit signed integer range. Example 1: Given nums = [1, -1, 5, -2, 3], … Read more
Given two sparse matrices A and B, return the result of AB. You may assume that A’s column number is equal to B’s row number. 1. Naive Method We can implement Sum(A_ik * B_kj) -> C_ij as a naive solution. public int[][] multiply(int[][] A, int[][] B) { //validity check int[][] C = new int[A.length][B[0].length]; … Read more
Find the nth digit of the infinite integer sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, … For example, given 3, output should be 3. Given 11, output should be 0. (The 11th digit of the sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, … is a … Read more
Given a non-negative integer n which represents the number of LEDs that are currently on, return all possible times the watch could represent. Example: Input: n = 1 Return: [“1:00”, “2:00”, “4:00”, “8:00”, “0:01”, “0:02”, “0:04”, “0:08”, “0:16”, “0:32”] Accepted Java Solution public List<String> readBinaryWatch(int num) { List<String> result = new ArrayList<String>(); for(int i=0; … Read more
Given a non-negative integer num represented as a string, remove k digits from the number so that the new number is the smallest possible. Note: The length of num is less than 10002 and will be ≥ k. The given num does not contain any leading zero. Example 1: Input: num = “1432219”, k = … Read more
Given a 2d matrix, find a path from the top left corner to bottom right corner. Assume there exists at least one path, and you only need to find one valid path. You can move up, right, down, left at any position. For example, given [1, 0, 0, 0, 0] [1, 0, 1, 1, 1] … Read more
Given an encoded string, return it’s decoded string. For example, given “3[a2[b]]”, return “abbabbabb”. https://leetcode.com/problems/decode-string/ Java Solution The key to solve this problem is convert the string to a structured data structure and recursively form the return string. class Solution { public String decodeString(String s) { Stack<Exp> stack = new Stack<>(); Exp e = … Read more
Find the length of the longest substring T of a given string (consists of lowercase letters only) such that every character in T appears no less than k times. Example 1: Input: s = “aaabb”, k = 3 Output: 3 The longest substring is “aaa”, as ‘a’ is repeated 3 times. Java Solution This problem … Read more
A character in UTF8 can be from 1 to 4 bytes long, subjected to the following rules: For 1-byte character, the first bit is a 0, followed by its unicode code. For n-bytes character, the first n-bits are all one’s, the n+1 bit is 0, followed by n-1 bytes with most significant 2 bits being … Read more
Design a Snake game that is played on a device with screen size = width x height. Play the game online if you are not familiar with the game. The snake is initially positioned at the top left corner (0,0) with length = 1 unit. You are given a list of food’s positions in row-column … Read more
https://leetcode.com/problems/longest-absolute-file-path/ Java Solution 1 class Node{ int level; int len; public Node(int lev, int len){ this.level = lev; this.len = len; } } public class Solution { public int lengthLongestPath(String input) { if(input==null||input.length()==0) return 0; int max=0; String[] arr = input.split("\n"); Stack<Node> stack = new Stack<Node>(); for(int i=0; i<arr.length; i++){ … Read more