Leetcode Perfect Squares Java Solution

Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, …) which sum to n. Example 1: Input: n = 12 Output: 3 Explanation: 12 = 4 + 4 + 4. Example 2: Input: n = 13 Output: 2 Explanation: 13 = 4 + 9. Solution: We will solve…… Continue reading Leetcode Perfect Squares Java Solution

Leetcode Regular Expression Matching Java Solution

Given an input string (s) and a pattern (p), implement regular expression matching with support for ‘.’ and ‘*’. ‘.’ Matches any single character. ‘*’ Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Note: s could be empty and contains only lowercase letters a-z.p could be empty and contains only lowercase letters a-z, and…… Continue reading Leetcode Regular Expression Matching Java Solution

Leetcode ZigZag Conversion Java Solution

The string “PAYPALISHIRING” is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N A P L S I I G Y I R And then read line by line: “PAHNAPLSIIGYIR” Write the code that will take…… Continue reading Leetcode ZigZag Conversion Java Solution

Leetcode Sum Root to Leaf Numbers Java Solution

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. An example is the root-to-leaf path 1->2->3 which represents the number 123. Find the total sum of all root-to-leaf numbers. Note: A leaf is a node with no children. Example: Input: [1,2,3] 1 / \ 2 3 Output: 25 Explanation: The root-to-leaf path 1->2 represents…… Continue reading Leetcode Sum Root to Leaf Numbers Java Solution

Leetcode Find the Duplicate Number Solution Java Solution

Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one. Example 1: Input: [1,3,4,2,2] Output: 2 Example 2: Input: [3,1,3,4,2] Output: 3 Note: You must not modify the array (assume the array is read…… Continue reading Leetcode Find the Duplicate Number Solution Java Solution

Leetcode Unique Binary Search Trees Java Solution

Given n, how many structurally unique BST’s (binary search trees) that store values 1 … n? Example: Input: 3 Output: 5 Explanation: Given n = 3, there are a total of 5 unique BST’s: 1 3 3 2 1 \ / / / \ \ 3 2 1 1 3 2 / / \ \ 2 1 2 3…… Continue reading Leetcode Unique Binary Search Trees Java Solution

Leetcode Count Complete Tree Nodes Java Solution

Given a complete binary tree, count the number of nodes. Note: Definition of a complete binary tree from Wikipedia:In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.…… Continue reading Leetcode Count Complete Tree Nodes Java Solution

Leetcode Single Number II Java Solution

Given a non-empty array of integers, every element appears three times except for one, which appears exactly once. Find that single one. Note: Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory? Example 1: Input: [2,2,3,2] Output: 3 Example 2: Input: [0,1,0,1,0,1,99] Output: 99 Solution 1: We will use a HashMap and…… Continue reading Leetcode Single Number II Java Solution

Leetcode Dungeon Game Java Solution

The demons had captured the princess (P) and imprisoned her in the bottom-right corner of a dungeon. The dungeon consists of M x N rooms laid out in a 2D grid. Our valiant knight (K) was initially positioned in the top-left room and must fight his way through the dungeon to rescue the princess. The…… Continue reading Leetcode Dungeon Game Java Solution

Leetcode 59 Spiral Matrix II Java Solution

Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order. Example: Input: 3 Output: [ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ] ] Solution 1: class Solution { public int[][] generateMatrix(int num) { int[][] spiralMatrix = new int[num][num]; int m =…… Continue reading Leetcode 59 Spiral Matrix II Java Solution