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[LeetCode] 54. Spiral Matrix

Given an m x n matrix, return all elements of the matrix in spiral order. Example 1:Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]Output: [1,2,3,6,9,8,7,4,5] Example 2:Input: matrix = [[1,2,3,4],

2020-02-14

#leetcode #array #java #javascript #matrix #simulation

[LeetCode] 48. Rotate Image

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise). You have to rotate the image in-place, which means you have to modify the input 2D matrix directly.

2020-02-14

#leetcode #array #java #javascript #matrix

[LeetCode] 134. Gas Station

There are n gas stations along a circular route, where the amount of gas at the ith station is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith stat

2020-02-13

#leetcode #array #java #javascript #greedy #math

[LeetCode] 70. Climbing Stairs

You are climbing a staircase. It takes n steps to reach to the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Note: Given n will be a positive in

2020-02-13

#leetcode #java #math #dynamic programming #memorization

[LeetCode] 107. Binary Tree Level Order Traversal II

Given the root of a binary tree, return the bottom-up level order traversal of its nodes’ values. (i.e., from left to right, level by level from leaf to root). Example 1:Input: root = [3,9,20,nul

2020-02-11

#leetcode #java #tree #bfs

[LeetCode] 98. Validate Binary Search Tree

Given the root of a binary tree, determine if it is a valid binary search tree (BST). A valid BST is defined as follows:The left subtree of a node contains only nodes with keys less than the node’s ke

2020-01-31

#leetcode #java #javascript #tree #inorder #bst

938. Range Sum of BST

Given the root node of a binary search tree and two integers low and high, return the sum of values of all nodes with a value in the inclusive range [low, high]. Example 1:Input: root = [10,5,15,

2020-01-30

#leetcode #java #tree #recursion #bst

[LeetCode] 169. Majority Element

Given an array nums of size n, return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the

2020-01-28

#leetcode #array #hashmap #java #javascript #math

[LeetCode] 49. Group Anagrams

Given an array of strings strs, group the anagrams together. You can return the answer in any order. An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typ

2020-01-24

#leetcode #array #hashmap #java #javascript #counting sort

[LeetCode] 451. Sort Characters By Frequency

Given a string s, sort it in decreasing order based on the frequency of characters, and return the sorted string. Example 1:Input: s = “tree”Output: “eert”Explanation: ‘e’ appears twice while ‘r’

2020-01-23

#leetcode #hashmap #java #sort #bucket sort #string #heap