꿈꾸는공학도

https://leetcode.com/problems/binary-tree-postorder-traversal/?envType=daily-question&envId=2024-09-04Given the root of a binary tree, return the postorder traversal of its nodes' values. Example 1:Input: root = [1,null,2,3]Output: [3,2,1]Explanation:Example 2:Input: root = [1,2,3,4,5,null,8,null,null,6,7,9]Output: [4,6,7,5,2,9,8,3,1]Explanation:Example 3:Input: root = []Output: []Example 4:Inpu..

Given an array of integers nums, sort the array in increasing order based on the frequency of the values. If multiple values have the same frequency, sort them in decreasing order.Return the sorted array. Example 1:Input: nums = [1,1,2,2,2,3]Output: [3,1,1,2,2,2]Explanation: '3' has a frequency of 1, '1' has a frequency of 2, and '2' has a frequency of 3.Example 2:Input: nums = [2,3,1,3,2]Output..

https://leetcode.com/problems/sum-of-digits-of-string-after-convert/description/?envType=daily-question&envId=2024-09-03You are given a string s consisting of lowercase English letters, and an integer k.First, convert s into an integer by replacing each letter with its position in the alphabet (i.e., replace 'a' with 1, 'b' with 2, ..., 'z' with 26). Then, transform the integer by replacing it w..

https://leetcode.com/problems/merge-two-binary-trees/description/You are given two binary trees root1 and root2.Imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not. You need to merge the two trees into a new binary tree. The merge rule is that if two nodes overlap, then sum node values up as the new value of the merged nod..

# Definition for a binary tree node.# class TreeNode:# def __init__(self, val=0, left=None, right=None):# self.val = val# self.left = left# self.right = rightclass Solution: def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]: ans = [] self.dfs(root, ans, 0) return ans def dfs(self, node, ans, lv): if not node: ..

https://leetcode.com/problems/find-the-student-that-will-replace-the-chalk/description/?envType=daily-question&envId=2024-09-02There are n students in a class numbered from 0 to n - 1. The teacher will give each student a problem starting with the student number 0, then the student number 1, and so on until the teacher reaches the student number n - 1. After that, the teacher will restart the pr..

https://leetcode.com/problems/add-one-row-to-tree/?envType=daily-question&envId=2024-08-23Given the root of a binary tree and two integers val and depth, add a row of nodes with value val at the given depth depth.Note that the root node is at depth 1.The adding rule is:Given the integer depth, for each not null tree node cur at the depth depth - 1, create two tree nodes with value val as cur's l..

https://leetcode.com/problems/fraction-addition-and-subtraction/description/?envType=daily-question&envId=2024-08-23Given a string expression representing an expression of fraction addition and subtraction, return the calculation result in string format.The final result should be an irreducible fraction. If your final result is an integer, change it to the format of a fraction that has a denomin..

https://leetcode.com/problems/sqrtx/description/Given a non-negative integer x, return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well.You must not use any built-in exponent function or operator.For example, do not use pow(x, 0.5) in c++ or x ** 0.5 in python. Example 1:Input: x = 4Output: 2Explanation: The square root of 4 is 2, so w..

https://leetcode.com/problems/maximum-width-of-binary-tree/description/Given the root of a binary tree, return the maximum width of the given tree.The maximum width of a tree is the maximum width among all levels.The width of one level is defined as the length between the end-nodes (the leftmost and rightmost non-null nodes), where the null nodes between the end-nodes that would be present in a ..