leetcode

Given an array nums, write a function to move all 0's to the end of it while maintaining the relative order of the non-zero elements.

108 Convert Sorted Array to Binary Search Tree Given an array where elements are sorted in ascending order, convert it to a height balanced BST. For

내가 봐도 for문 남발에 넘 비효율적 코드Discuss에 있던 C Solution using freq counterfreqCounterS가 인덱스와 비슷한 역할을 한다고 생각..특정 알파벳이 몇번 등장했는지 비교를 통한 수행알파벳은 총 26개 이므로 배열의 크기도 2

Say you have an array prices for which the ith element is the price of a given stock on day i.Design an algorithm to find the maximum profit. You may

Given a column title as appear in an Excel sheet, return its corresponding column number.For example:맨처음 구상했던 건 두자리의 case까지만 가능했음왜 저따구로 생각했는진 모르겠지만..자

Given an array of integers, find if the array contains any duplicates.Your function should return true if any value appears at least twice in the arra

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.For example, 2 is written as II in Roman numeral, just two one's add

Merge two sorted linked lists and return it as a new sorted list. The new list should be made by splicing together the nodes of the first two lists.문제

Given an array nums containing n distinct numbers in the range 0, n, return the only number in the range that is missing from the array.Follow up: Cou

Given two arrays, write a function to compute their intersection.맨첨엔 당연히 이중 for 문이 생각났지만^^ 이제 얘랑 이별했으므로..'in' 을 사용해서 반복문은 하나만 사용했다('in': 반복문 없이 배열 안에

Write a function that takes an unsigned integer and returns the number of '1' bits it has (also known as the Hamming weight).Note that in some languag

Say you have an array for which the ith element is the price of a given stock on day i.If you were only permitted to complete at most one transaction

Write an algorithm to determine if a number n is "happy".A happy number is a number defined by the following process: Starting with any positive integ

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 t

Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.Follow up: If

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).For example, this binary tree 1,2,2,3,4,4,3 is symmetric

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.push(x) -- Push element x onto stack.pop() -- Removes

Given a sorted array nums, remove the duplicates in-place such that each element appears only once and returns the new length.Do not allocate extra sp

Given a non-empty array of decimal digits representing a non-negative integer, increment one to the integer.The digits are stored such that the most s

The count-and-say sequence is a sequence of digit strings defined by the recursive formula:countAndSay(1) = "1"countAndSay(n) is the way you would "sa

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 y

160. Intersection of Two Linked Lists - python3 Write a program to find the node at which the intersection of two singly linked lists begins. For exa

Given an integer n, return true if it is a power of three. Otherwise, return false.An integer n is a power of three, if there exists an integer x such

어제 배운 뒷목잡고 쓰러질뻔한 초간단 코드를 참고해서 시작했다그 코드의 핵심은 한칸씩 움직이는 포인터와 먼저 앞서나가는 포인터라고 생각해서hB는 걍 휙휙 지나가라고 .next.next를 해줌head.next 가 없는 케이스에서 자꾸 오류 난리나서 조건문으로 제한을 많이

88. Merge Sorted Array - python3 Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array. Note: The number of el

Reverse bits of a given 32 bits unsigned integer.Note:Note that in some languages such as Java, there is no unsigned integer type. In this case, both

Given a singly linked list, determine if it is a palindrome.링크드 리스트가 아니라 그냥 배열 형태의 리스트였으면 절반으로 나눠서 비교하면 됐을텐데...하는 생각으로 head 를 한번 훑으면서 arr 리스트에 모든 값을 넣

Given a string s containing just the characters '(', ')', '{', '}', '' and '', determine if the input string is valid.An input string is valid if:Open

Given an integer n, return the number of trailing zeroes in n!.Follow up: Could you write a solution that works in logarithmic time complexity?맨 처음 생각

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.Note: For the purpose of this problem, we

Write a function to find the longest common prefix string amongst an array of strings.If there is no common prefix, return an empty string "".첨에 문제 이해

Implement strStr().Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.Clarification:What should w

Given a non-negative integer x, compute and return the square root of x.Since the return type is an integer, the decimal digits are truncated, and onl

Given a 32-bit signed integer, reverse digits of an integer.Note:Assume we are dealing with an environment that could only store integers within the 3

204. Count Primes - python3 Count the number of prime numbers less than a non-negative number, n. My Answer 1: Time Limit Exceeded (17 / 20 test case

투썸플레이스Best Time to Buy and Sell StockClimbing StairsunHappy numberIntersection of Two Linked Lists 극혐솔직히 이건.. 기억에 의존했읍니다Palindrome Linked List

94. Binary Tree Inorder Traversal - python3 Given the root of a binary tree, return the inorder traversal of its nodes' values. My Answer 1: Accepted

22. Generate Parentheses - python3 Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses. 내 머리는 너무나

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.22 번이랑 유사한 거 같은데 하나도 모르겠읍니다....

Given an integer array nums, return all possible subsets (the power set).The solution set must not contain duplicate subsets.permutations 트라우마가 24 시간도

347. Top K Frequent Elements - python3 Given a non-empty array of integers, return the k most frequent elements. My Answer 1: Accepted (Runtime: 92 m

230. Kth Smallest Element in a BST - python3 Given a binary search tree, write a function kthSmallest to find the kth smallest element in it. My Answ

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

Given an array nums of n integers where n > 1, return an array output such that outputi is equal to the product of all the elements of nums except nu

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.nums 정렬 후

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 rearrangi

Given a singly linked list, group all odd nodes together followed by the even nodes. Please note here we are talking about the node number and not the

Given an array of integers nums containing n + 1 integers where each integer is in the range 1, n inclusive.There is only one duplicate number in nums

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).BFS 中 level-order 순회 방식을 사용함레벨을 의

According to the Wikipedia's article: "The Game of Life, also known simply as Life, is a cellular automaton devised by the British mathematician John

Given a n x n matrix where each of the rows and columns are sorted in ascending order, find the kth smallest element in the matrix.Note that it is the

62. Unique Paths - python3 A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below). The robot can only move e

Given four lists A, B, C, D of integer values, compute how many tuples (i, j, k, l) there are such that Ai + Bj + Ck + Dl is zero.To make problem a bi

Given a nested list of integers, implement an iterator to flatten it.Each element is either an integer, or a list -- whose elements may also be intege

Given an integer array nums, design an algorithm to randomly shuffle the array.Implement the Solution class:Solution(int\[] nums) Initializes the obje

Given n non-negative integers a1, a2, ..., an , where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endp

Implement a trie with insert, search, and startsWith methods.아 쉽다쉬워했건만,,그렇게 비효율적으로 보이지도 않는거 같은데 런타임이 상당히 느리다..리스트 때문인듯?!딕셔너리를 이용한 방식TrieNode 를 이용한 방식T

Given a string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s.A palindrom

Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -.이 문제를 낸 의도가 무엇일까...이거 거의 창의력 문제 아닌지..\+- 연산자 쓰지 말래서 그냥

Given preorder and inorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.일단 다 insert 하고

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:Each row must contain the digi

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and

Given an array nums with n objects colored red, white, or blue, sort them in-place so that objects of the same color are adjacent, with the colors in

Implement the RandomizedSet class:bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present, fals

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any

Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.반복문 n 개 중첩이 떠올라서... 루션이 불렀읍

You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. The binary tree has the following defin

Given an m x n 2d grid map of '1's (land) and '0's (water), return the number of islands.An island is surrounded by water and is formed by connecting

Given the head of a linked list, return the list after sorting it in ascending order.Follow up: Can you sort the linked list in O(n logn) time and O(1

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.According to the definition of LCA on Wikipedia: “The lowest

Given an m x n matrix. If an element is 0, set its entire row and column to 0. Do it in-place.Follow up:A straight forward solution using O(mn) space

There are a total of numCourses courses you have to take, labeled from 0 to numCourses-1.Some courses may have prerequisites, for example to take cour

Write an efficient algorithm that searches for a target value in an m x n integer matrix. The matrix has the following properties:Integers in each row

A peak element is an element that is strictly greater than its neighbors.Given an integer array nums, find a peak element, and return its index. If th

Given a string s and an integer k, return the length of the longest substring of s such that the frequency of each character in this substring is grea

Given an integer array nums, return the length of the longest strictly increasing subsequence.A subsequence is a sequence that can be derived from an

Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine if s can be segmented into a space-separated sequ

There are a total of n courses you have to take labelled from 0 to n - 1.Some courses may have prerequisites, for example, if prerequisitesi = ai, bi

Given an integer array nums, return true if there exists a triple of indices (i, j, k) such that i < j < k and numsi < numsj < numsk. If n

There are n gas stations along a circular route, where the amount of gas at the ith station is gasi.You have a car with an unlimited gas tank and it c

Given an array of intervals where intervalsi = starti, endi, merge all overlapping intervals, and return an array of the non-overlapping intervals tha

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.Return a deep copy

Evaluate the value of an arithmetic expression in Reverse Polish Notation.Valid operators are +, -, \*, /. Each operand may be an integer or another e

Given a string s which represents an expression, evaluate this expression and return its value. The integer division should truncate toward zero.이것도 1

34. Find First and Last Position of Element in Sorted Array Given an array of integers nums sorted in ascending order, find the starting and ending po

322. Coin Change You are given coins of different denominations and a total amount of money amount. Write a function to compute the fewest number of c

Given an array, rotate the array to the right by k steps, where k is non-negative.Follow up:Try to come up as many solutions as you can, there are at

79. Word Search Given an m x n board and a word, find if the word exists in the grid. The word can be constructed from letters of sequentially adjace

You are given an integer array nums sorted in ascending order (with distinct values), and an integer target.Suppose that nums is rotated at some pivot

Given the head of a linked list, remove the nth node from the end of the list and return its head.Follow up: Could you do this in one pass?맨 앞이 제거되는 경

Design a data structure that follows the constraints of a Least Recently Used (LRU) cache.Implement the LRUCache class:LRUCache(int capacity) Initiali

Given an array of non-negative integers nums, you are initially positioned at the first index of the array.Each element in the array represents your m

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes conta

Given an m x n matrix, return all elements of the matrix in spiral order.이거.. 예시 그림대로 append 하도록 해보려 했는데 생각보다 잘 안됨..ㅎ나의 생각과 가장 일치한 솔루션...row, col 의 be

Given a string s, find the length of the longest substring without repeating characters.why... ㅎ6상 2中 for 곰ㅇi.. LㅓbooEㅓ 생각..ㄴr는girlㄱㄱㅏ...☆★비효율의 끝판왕 모셨

Given an integer array nums, find the contiguous subarray within an array (containing at least one number) which has the largest product.어김없이 이중 for 문

Implement pow(x, n), which calculates x raised to the power n (i.e. xn).양수면 x 의 n 승 반환, 음수면 1/x 의 -n 승 반환반복문으로 하나하나 곱해주는게 가장 느렸다..이거도 올리면 극딜 당할 거 같고..

Given an integer array nums, reorder it such that nums0 < nums1 > nums2 < nums3....You may assume the input array always has a valid answer.그냥 몰

Given a list of non-negative integers nums, arrange them such that they form the largest number.Note: The result may be very large, so you need to ret

Given a string s, return the longest palindromic substring in s.전에 풀었던 131. Palindrome Partitioning 문제를 응용해서 어찌 해보려했지만.. 실패DP 를 사용한 방식처음엔 n\*n 만큼 Fals

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 cont

Given a 2D board containing 'X' and 'O' (the letter O), capture all regions surrounded by 'X'.A region is captured by flipping all 'O's into 'X's in t

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the s

A message containing letters from A-Z can be encoded into numbers using the following mapping:'A' -> "1"'B' -> "2"...'Z' -> "26"To decode an encoded m

Given two integers dividend and divisor, divide two integers without using multiplication, division, and mod operator.Return the quotient after dividi

Given two integers representing the numerator and denominator of a fraction, return the fraction in string format.If the fractional part is repeating,

Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer (similar to C/C++'s atoi function).The algorithm for myAto

Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.left 값

Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.nums 를 sort 한 후 연속된 숫자 찾는 식으로 함..연속되면 temp+1

Median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value. So the median is the mean of the two

239. Sliding Window Maximum You are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the arr

329. Longest Increasing Path in a Matrix Given an m x n integers matrix, return the length of the longest increasing path in matrix. From each cell,

You are given an array of k linked-lists lists, each linked-list is sorted in ascending order.Merge all the linked-lists into one sorted linked-list a

315. Count of Smaller Numbers After Self You are given an integer array nums and you have to return a new counts array. The counts array has the prope

Given n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the hist

Given an m x n board of characters and a list of strings words, return all words on the board.Each word must be constructed from letters of sequential

Given two strings s and t, return the minimum window in s which will contain all the characters in t. If there is no such window in s that covers all

A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Given the locations and

Given an unsorted integer array nums, find the smallest missing positive integer.1 이 없으면 First Missing Positive 는 무조건 1 이므로 1 의 유무부터 확인가장 마지막 케이스가 \[2

A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words such that:The first word in the seque

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 i

Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, add spaces in s to construct a sentence where each word is

4. Median of Two Sorted Arrays Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays. Foll

Given an input string (s) and a pattern (p), implement regular expression matching with support for '.' and '\*' where: '.' Matches any single charact

Given an input string (s) and a pattern (p), implement wildcard pattern matching with support for '?' and '\*' where:'?' Matches any single character.

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.y = ax + b 형태를 이용해서 점마다 기울기 구해서 하면 될 거 같기도 한데...이 기

These problems may require you to implement a given interface of a class, and may involve using one or more data structures. These are great exercises

Most of the math questions asked in interviews do not require math knowledge beyond middle school level. We recommend: Excel Sheet Column Number, Pow

Here are some other questions that do not fit in other categories.We recommend: Majority Element, Find the Celebrity and Task Scheduler.Given two inte

Given an array nums of n integers where numsi is in the range 1, n, return an array of all the integers in the range 1, n that do not appear in nums.F

https://leetcode.com/problems/roman-to-integer/딕셔너리에 symbol 정리, subtract 에 해당하는 symbol 들도 정리연속된 두 문자가 subtract 에 포함되면 subtract 값으로 계산아니면 원래 symbo

https://leetcode.com/problems/two-sum/target - nums\[i] 이 있으면 index 찾아서 return저번에 풀었던 방식...ㅎdic 에 target - nums\[i] 이름으로 대응하는 값의 인덱스를 넣어줌https&#x

https://leetcode.com/problems/valid-parentheses/여는 괄호들은 stack 에 쌓아주고닫는 괄호를 만나면 stack\[-1] 과 대응하는지 확인해서 유효한지 판단짝을 찾지 못한 괄호가 stack 에 남아있으면 Falsehtt

https://leetcode.com/problems/remove-duplicates-from-sorted-array/prev 값이랑 비교해서 같으면 뒤로 쭉 옮겨주기그나마 적게 움직이려고 right 변수 설정해서 옮길 위치 정해줌decreasing 하면 br

https://leetcode.com/problems/maximum-subarray/ans 는 nums 의 최댓값으로 default 설정sub 에 값을 하나씩 더해가면서지금까지의 합이 자기 자신보다 큰 경우만 ans update자기 자신보다 작아지면 볼 필요가

https://leetcode.com/problems/sqrtx/여기서도 Binary Search 를...?!1 보다 큰 숫자들의 제곱근은 모두 n/2 보다 작은 값을 갖기 때문에 high =

https://leetcode.com/problems/merge-sorted-array/둘이 합해서 sort 후 n 만큼의 0 없애주기 큰 값부터 역순으로 비교해서 nums1 의 맨 뒷자리부터 채워주기nums1 과 nums2 중에 큰

https://leetcode.com/problems/symmetric-tree/루트의 left 와 right 를 나눠서left 는 left -> right 순으로 보면서 value 를 left 에 저장right 는 right -> left 순으로 보면서 va

https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/처음에는 root 값과 비교해서 작으면 left 에 크면 right 에 노드를 생성해줬는데그러면 height-balanced bi

https://leetcode.com/problems/best-time-to-buy-and-sell-stock/더 작은 값이 나오면 buybuy 보다 큰 값들과의 차이를 ans 에 update예전에 풀던 게 강력했는지 stock 문제는 익숙~https&#x3A

https://leetcode.com/problems/single-number/Counter 로 1 번 나오는 값 찾아주기You must implement a solution with a linear runtime complexity and use only c

https://leetcode.com/problems/linked-list-cycle/거북이와 토끼인가 slow and fast 를 이용해서h1 은 한 노드씩 천천히 움직이고 h2 는 두 노드씩 빠르게 움직여서둘이 같은 노드를 가리키면 return True이게

https://leetcode.com/problems/intersection-of-two-linked-lists/hA 와 hB 의 길이가 다를 수 있기 때문에모두 한 노드씩 움직이다가 끝이 나면 A -> B, B -> A 헤드를 보도록 함if hA.next i

https://leetcode.com/problems/majority-element/Counter 로 n // 2 보다 큰 횟수만큼 나온 key returnn // 2 만큼은 보장된거니까 정렬 후 n // 2 번째 값 return한줄로도 가능~https&#x3

https://leetcode.com/problems/factorial-trailing-zeroes/1 부터 n 까지의 팩토리얼을 구해서 string 으로 바꾸고 맨 뒤부터 0 의 개수 세주기logarithmic 이 아니라서 매우 느리다..^^어떻게 하면 더

https://leetcode.com/problems/number-of-1-bits/n 을 2 진수로 바꾼 후, 1 의 개수 세주기bin() 함수를 사용하면 맨 앞에 0b 가 붙는다2 로 계속 나누면서 나머지 값 1 만 ans 에 더해주기2 로 나누는 건 너무

https://leetcode.com/problems/count-primes/소수들을 primes 에 넣어주면서각 숫자마다 약수가 primes 에 존재하는지 확인해서없으면 소수니까 primes 에 넣어주고마지막에 길이 return2 ~ sqrt(n) 의 범위로

https://leetcode.com/problems/contains-duplicate/Counter 로 중복 되는 숫자 찾기그냥 딕셔너리 써서 이미 존재하는 숫자인지 확인해도 된다if nums\[i] in nums\[i+1:] 로 확인하면 타임리밋 걸림htt

https://leetcode.com/problems/delete-node-in-a-linked-list/주어지는 node 는 항상 마지막 노드가 아니므로 n = node.nextnode 부터 보면서 next 값을 node 에 덮어씌움저번에 푼 건데그냥 현재

https://leetcode.com/problems/missing-number/정렬해서 0 ~ n 까지 연속인지 확인연속하지 않으면 끊긴 값 return끝까지 봤으면 마지막 값 + 1 return이 외에도 in 을 사용하는 방식도 해봤지만Follow up:

https://leetcode.com/problems/power-of-three/n 을 3 으로 계속 나눴을 때, 3 의 제곱수라면 최종적으로 1 이 됨마지막 n 이 1 인지 판단해서 T/F returnFollow up: Could you solve it wi

https://leetcode.com/problems/intersection-of-two-arrays-ii/길이가 더 작은 nums 를 nums1 로 잡아줌nums1 값이 nums2 에 있으면 nums2 에서 제거 & ans 에 추가아니면 Counter 로 n

https://leetcode.com/problems/fizz-buzz/문제 고대로15 의 배수면 "FizzBuzz"3 의 배수면 "Fizz"5 의 배수면 "Buzz"나머지는 숫자 그대로 넣어주기https://leetcode.com/problems/l

198. House Robber https://leetcode.com/problems/house-robber/ My answer 1: Accepted (Runtime: 28 ms - 85.65% / Memory Usage: 14.4 MB - 19.99%) 길이 2

https://leetcode.com/problems/implement-trie-prefix-tree/words 에는 insert 된 word 들 저장prefix 에는 word 마다 모든 prefix 들을 저장insert)이미 본 단어가 아닐때만 add 하도록

https://leetcode.com/problems/basic-calculator-ii/우선 공백들 모두 제거 => replacestack 에 숫자, 연산자를 구분해서 저장=> 한자리 숫자만 있는게 아니기 때문에 num 에 숫자를 계속 저장해두고 연산자를 만

https://leetcode.com/problems/product-of-array-except-self/먼저 p, zero 를 구함p: 0 을 제외한 전체 곱zero: 0 의 개수다시 nums 를 보면서0 이 한개일 때는 0 을 제외한 나머지 위치는 모두 0

253. Meeting Rooms II https://leetcode.com/problems/meeting-rooms-ii/ https://www.lintcode.com/problem/919/ My Answer 1: Accepted ( 277. Find the Ce

https://leetcode.com/problems/inorder-successor-in-bst/https://www.lintcode.com/problem/448/if root.val < p.val:=> 왼쪽은 볼 필요가 없으니까 root.ri

https://leetcode.com/problems/number-of-islands/1 을 만나면 해당 1 과 연결된 모든 1 들을 0 으로 바꿔주면서 count주의할 점은 string 숫자로 저장되어있다는 점이다1 을 만나면 해당 좌표를 q 에 넣고 상하좌