[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
[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
[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
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,
[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
[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
[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’
[LeetCode] 138. Copy List with Random Pointer
A linked list of length n is given such that each node contains an additional random pointer, which could point to any node in the list, or null. Construct a deep copy of the list. The deep copy shoul