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난이도 [ 👿 😊 🤔 ] Hard Medium Easy 문제 설명 There are n rooms labeled from 0 to n - 1 and all the rooms are locked except for room 0. Your goal is to visit all the rooms. However, you cannot enter a locked room without having its key. When you visit a room, you may find a set of distinct keys in it. Each key has a number on it, denoting which room it unlocks, and you can take all of them with you to un..

난이도 [ 🤔 ] Medium 문제 설명 Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible, keep answer[i] == 0 instead. 일일 온도가 입력된 배열에서 더 따듯해지는 날까지의 일 수의 배열을 반환하면된다. 없으면 0으로 리턴한다. 입출력 예 Example 1: Input: temp..

난이도 [ 🤔 ] Medium 문제 설명 Evaluate the value of an arithmetic expression in Reverse Polish Notation. Valid operators are +, -, *, and /. Each operand may be an integer or another expression. Note that division between two integers should truncate toward zero. It is guaranteed that the given RPN expression is always valid. That means the expression would always evaluate to a result, and there will n..

난이도 [ 😊 ] Easy 문제 설명 Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push, peek, pop, and empty). Implement the MyQueue class: void push(int x) Pushes element x to the back of the queue. int pop() Removes the element from the front of the queue and returns it. int peek() Returns the element at the front ..

난이도 [ 🤔 ] Medium 문제 설명 Given two strings text1 and text2, return the length of their longest common subsequence. If there is no common subsequence, return 0. A subsequence of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters. For example, "ace" is a subsequence of "abcde". A commo..

난이도 [ 🤔 ] Medium 문제 설명 Given an integer array nums, find a subarray that has the largest product, and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. 연속된 element 중 곱했을 때, 가장큰 수를 return 한다. 입출력 예 Example 1: Input: nums = [2,3,-2,4] Output: 6 Explanation: [2,3] has the largest product 6. Example 2: Input: nums = [-2,0,-1] Output: 0 Explanation: The..

난이도 [ 🤔 ] Medium 문제 설명 You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums represent..

난이도 [ 🤔 ] Medium 문제 설명 Given an n x n array of integers matrix, return the minimum sum of any falling path through matrix. A falling path starts at any element in the first row and chooses the element in the next row that is either directly below or diagonally left/right. Specifically, the next element from position (row, col) will be (row + 1, col - 1), (row + 1, col), or (row + 1, col + 1). n ..

난이도 [ 😊 ] Easy 문제 설명 You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? n 계단을 올라가는데, 1 또는 2칸 씩 올라 갈 때, 모든 경우의 수는 얼마인가? 입출력 예 Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation..

난이도 [ 👿 ] Hard 문제 설명 A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree, return the maximum path sum of any non..

난이도 [ 🤔 ] Medium 문제 설명 Given the root of a binary tree, split the binary tree into two subtrees by removing one edge such that the product of the sums of the subtrees is maximized. Return the maximum product of the sums of the two subtrees. Since the answer may be too large, return it modulo 109 + 7. Note that you need to maximize the answer before taking the mod and not after taking it. 문제가 좀 복..

난이도 [ 🤔 ] Medium 문제 설명 Given the root of a binary tree, find the maximum value v for which there exist different nodes a and b where v = |a.val - b.val| and a is an ancestor of b. A node a is an ancestor of b if either: any child of a is equal to b or any child of a is an ancestor of b. 이진트리의 상위, 하위 노드의 a-b 의 최대값을 찾는 문제다. 입출력 예 Example 1: Input: root = [8,3,10,1,6,null,14,null,null,4,7,13] Outpu..

난이도 [ 😊 ] Easy 문제 설명 Consider all the leaves of a binary tree, from left to right order, the values of those leaves form a leaf value sequence. For example, in the given tree above, the leaf value sequence is (6, 7, 4, 9, 8). Two binary trees are considered leaf-similar if their leaf value sequence is the same. Return true if and only if the two given trees with head nodes root1 and root2 are le..

난이도 [ 😊 ] Easy 문제 설명 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]. 2진 트리의 노드 값이 low, high 범위에 들어오면 모두 더해서 return 한다. 입출력 예 Example 1: Input: root = [10,5,15,3,7,null,18], low = 7, high = 15 Output: 32 Explanation: Nodes 7, 10, and 15 are in the range [7, 15]. 7 + 10 + 15 = 32. Exam..

난이도 [ 🤔 ] Medium 문제 설명 Given the head of a singly linked list, group all the nodes with odd indices together followed by the nodes with even indices, and return the reordered list. The first node is considered odd, and the second node is even, and so on. Note that the relative order inside both the even and odd groups should remain as it was in the input. You must solve the problem in O(1) extra..

난이도 [ 😊 ] Easy 문제 설명 Given the head of a singly linked list, return the middle node of the linked list. If there are two middle nodes, return the second middle node. 단일 linked List 를 준다. list의 중간 부터 return하는데, 중간이 2개 인 경우(짝수 length) 일땐, 2번째 중간 값 부터 return 해준다. 입출력 예 Example 1: Input: head = [1,2,3,4,5] Output: [3,4,5] Explanation: The middle node of the list is node 3. Example 2: Input: head = [..

난이도 [ 🤔 ] Medium 문제 설명 You are given a 0-indexed integer array nums of length n. The average difference of the index i is the absolute difference between the average of the first i + 1 elements of nums and the average of the last n - i - 1 elements. Both averages should be rounded down to the nearest integer. Return the index with the minimum average difference. If there are multiple such indice..

난이도 [ 🤔 ] Medium 문제 설명 Given a string s, sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string. Return the sorted string. If there are multiple answers, return any of them. 문자열 s에 문자가 등장횟수만큼 내림차순 정렬한다. aaaccc, cccaaa 는 둘다 정답이란다. 숫자만 신경쓰면 된다. 입출력 예 Example 1: Input: s = "tree" Output: "eert" Explanation: ..

난이도 [ 🤔 ] Medium 문제 설명 Two strings are considered close if you can attain one from the other using the following operations: Operation 1: Swap any two existing characters. For example, abcde -> aecdb Operation 2: Transform every occurrence of one existing character into another existing character, and do the same with the other character. For example, aacabb -> bbcbaa (all a's turn into b's, and..

난이도 [ 😊 ] Easy 문제 설명 You are given a string s of even length. Split this string into two halves of equal lengths, and let a be the first half and b be the second half. Two strings are alike if they have the same number of vowels ('a','e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'). Notice that s contains uppercase and lowercase letters. Return true if a and b are alike. Otherwise, return false. 짝수 ..