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Leet Code 83. Remove Duplicates from Sorted List [Easy] Problem: Given a sorted linked list, delete all duplicates such that each element appear only once. Example 1: Input: 1->1->2 Output: 1->2 Example 2: Input: 1->1->2->3->3 Output: 1->2->3 -Summary- 1. Set root as head first. 2. Move the head and compare the current value with the next value. If it is the same, point next to next.next. Otherwise, move head to the next. 3. Return root -Code- # Defi.. 공감수 0 댓글수 1 2020. 9. 8.
LeetCode 561. Array Partition I [Easy] Problem: Given an array of 2n integers, your task is to group these integers into n pairs of integer, say (a1, b1), (a2, b2), ..., (an, bn) which makes sum of min(ai, bi) for all i from 1 to n as large as possible. Example 1: Input: [1,4,3,2] Output: 4 Explanation: n is 2, and the maximum sum of pairs is 4 = min(1, 2) + min(3, 4). Note: n is a positive integer, which is in the range of [1, 10000.. 공감수 0 댓글수 0 2020. 8. 26.
LeetCode 15. 3Sum [Medium] Problem: 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 sum of zero. Note: The solution set must not contain duplicate triplets. Example: Summary: Using a two-pointer move left and the right pointer to compare the sum of three-element. Code: class Solution: def threeSum(self, nums: List[int]) ->.. 공감수 0 댓글수 0 2020. 8. 25.
LeetCode 42. Trapping Rain Water [Hard] Problem: Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining. The above elevation map is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped. Thanks Marcos for contributing this image! Example: Input: [0,1,0,2,1,0,1,3,2,1,2,1] Output: .. 공감수 0 댓글수 1 2020. 8. 24.
LeetCode 49. Group Anagrams Problem: Given an array of strings, group anagrams together. Example: Input: ["eat", "tea", "tan", "ate", "nat", "bat"], Output: [ ["ate","eat","tea"], ["nat","tan"], ["bat"] ] Summary: 1. Create a defaultdict(list) to save the sorted word as a key in list format. 2. For each word, sort the word so that any anagram word would be saved in a list under same key. 3. return with all values saved in .. 공감수 0 댓글수 0 2020. 8. 19.
LeetCode 819. Most Common Word Problem: Given a paragraph and a list of banned words, return the most frequent word that is not in the list of banned words. It is guaranteed there is at least one word that isn't banned, and that the answer is unique. Words in the list of banned words are given in lowercase, and free of punctuation. Words in the paragraph are not case sensitive. The answer is in lowercase. Example: Input: para.. 공감수 0 댓글수 0 2020. 8. 18.
LeetCode 937. Reorder Data in Log Files Problem: You have an array of logs. Each log is a space delimited string of words. For each log, the first word in each log is an alphanumeric identifier. Then, either: Each word after the identifier will consist only of lowercase letters, or; Each word after the identifier will consist only of digits. We will call these two varieties of logs letter-logs and digit-logs. It is guaranteed that eac.. 공감수 0 댓글수 0 2020. 8. 17.
LeetCode 628. Maximum Product of Three Numbers Problem: Given an integer array, find three numbers whose product is maximum and output the maximum product. Example 1: Input: [1,2,3] Output: 6 Example 2: Input: [1,2,3,4] Output: 24 Note: The length of the given array will be in range [3,104] and all elements are in the range [-1000, 1000]. Multiplication of any three numbers in the input won't exceed the range of 32-bit signed integer. -Summa.. 공감수 0 댓글수 0 2020. 7. 9.
LeetCode 91. Decode Ways Problem: A message containing letters from A-Z is being encoded to numbers using the following mapping:'A' -> 1 'B' -> 2 ... 'Z' -> 26 Given a non-empty string containing only digits, determine the total number of ways to decode it. Example 1: Input: "12" Output: 2 Explanation: It could be decoded as "AB" (1 2) or "L" (12). Example 2: Input: "226" Output: 3 Explanation: It could be decoded as "B.. 공감수 0 댓글수 0 2020. 6. 21.
LeetCode 226. Invert Binary Tree Problem: Invert a binary tree. Example: -Summary- Solved recursively 1. Until root node exist, we keep traverse left and right and change the left and right subtree by exchanging value. (By calling the function recursively) Here is another solution by solving this iteratively using stack. def invertTree(self, root): stack = [root] while stack: node = stack.pop() if node: node.left, node.right = .. 공감수 0 댓글수 0 2020. 6. 20.
Daily Coding Problem #5 Problem: cons(a, b) constructs a pair, and car(pair) and cdr(pair) returns the first and last element of that pair. For example, car(cons(3, 4)) returns 3, and cdr(cons(3, 4)) returns 4. Given this implementation of cons: def cons(a, b): def pair(f): return f(a, b) return pair Implement car and cdr. -Summary- def car(pair): def return_first(a, b): return a return pair(return_first) def cdr(pair).. 공감수 0 댓글수 0 2020. 6. 19.
Floor and Ceiling of a Binary Search Tree Problem: Given an integer k and a binary search tree, find the floor (less than or equal to) of k, and the ceiling (larger than or equal to) of k. If either does not exist, then print them as None. Here is the definition of a node for the tree. -Summary- 1. if root node is empty we return none value for both floor and ceil. 2. if root node is equal with k, return floor and cell with k value 3. i.. 공감수 0 댓글수 0 2020. 6. 19.
LeetCode 41. First Missing Positive Problem: Given an unsorted integer array, find the smallest missing positive integer. Example 1: Input: [1,2,0] Output: 3 Example 2: Input: [3,4,-1,1] Output: 2 Example 3: Input: [7,8,9,11,12] Output: 1 -Summary- 1. Set first positive integer as 1 --> posNum 2. loop-through the nums and check if posNum is in the nums list. (max int: 2^31 -1) - if there is, adding 1 more value to posNum and find .. 공감수 0 댓글수 0 2020. 6. 18.
LeetCode 665. Non-decreasing Array Problem: Given an array nums with n integers, your task is to check if it could become non-decreasing by modifying at most 1 element. We define an array is non-decreasing if nums[i] 공감수 0 댓글수 0 2020. 6. 18.
LeetCode 136. Single Number Problem: Given a non-empty array of integers, every element appears twice except for one. Find that single one. Note: Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory? Example 1: Input: [2,2,1] Output: 1 Example 2: Input: [4,1,2,1,2] Output: 4 -Summary- Using XOR Bit operation 1. Do XOR bit operation for all numbers 2. return the answer EX.. 공감수 0 댓글수 0 2020. 6. 17.
LeetCode 238. Product of Array Except Self [Array] Problem: Given an array nums of n integers where n > 1, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i]. Example: Input: [1,2,3,4] Output: [24,12,8,6] Constraint: It's guaranteed that the product of the elements of any prefix or suffix of the array (including the whole array) fits in a 32 bit integer. Note: Please solve it without div.. 공감수 0 댓글수 0 2020. 6. 16.
LeetCode 34. Find First and Last Position of Element in Sorted Array [Binary Search] Problem: Given an array of integers nums sorted in ascending order, find the starting and ending position of a given target value. Your algorithm's runtime complexity must be in the order of O(log n). If the target is not found in the array, return [-1, -1]. Example 1: Input: nums = [5,7,7,8,8,10], target = 8 Output: [3,4] Example 2: Input: nums = [5,7,7,8,8,10], target = 6 Output: [-1,-1] -Summ.. 공감수 0 댓글수 0 2020. 6. 13.
5. Longest Palindromic Substring [Strings, dynamic programming] Problems: Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000. Example 1: Input: "babad" Output: "bab" Note: "aba" is also a valid answer. Example 2: Input: "cbbd" Output: "bb" -Summary- Approach: Expand around the center 1. Two cases exist. - Palindrome with odd lengths of string (example: 'aba', 'abcba') --> where 1 character in th.. 공감수 1 댓글수 0 2020. 6. 11.
LeetCode 3. Longest Substring Without Repeating Characters [Sliding Window, Two-Pointers] Problems: Given a string, find the length of the longest substring without repeating characters. Example 1: Input: "abcabcbb" Output: 3 Explanation: The answer is "abc", with the length of 3. Example 2: Input: "bbbbb" Output: 1 Explanation: The answer is "b", with the length of 1. Example 3: Input: "pwwkew" Output: 3 Explanation: The answer is "wke", with the length of 3. Note that the answer mu.. 공감수 0 댓글수 0 2020. 6. 10.
LeetCode 2. Add Two Numbers [Linked List] Problem: 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 contain a single digit. Add the two numbers and return it as a linked list. You may assume the two numbers do not contain any leading zero, except the number 0 itself. Example: Input: (2 -> 4 -> 3) + (5 -> 6 -> 4) Output: 7 -> 0 -> 8 Explanation.. 공감수 0 댓글수 0 2020. 6. 9.
LeetCode 21. Merge Two Sorted Lists Problem: 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. Example: Input: 1->2->4, 1->3->4 Output: 1->1->2->3->4->4 -Summary- 1. Create a dummy and curr variables to track and merge the two lists. 2. Compare l1 and l2 value. 'curr' will connect to the less value. Update l1 or l2 depends on the res.. 공감수 0 댓글수 0 2020. 6. 1.
LeetCode 206. Reverse Linked List Problem: Reverse a singly linked list. Example: Input: 1->2->3->4->5->NULL Output: 5->4->3->2->1->NULL -Summary- 1. Keep track of current / prev (copy the original list in the curr and prev) 2. Update and move the head (original) 3. Return prev 정답을 보니 recursive 하게 푸는 방법도 있었다. leetcode.com/problems/reverse-linked-list/discuss/609282/Python-Recursion-Highly-Commented-(greater99) 모든 문제에 대한 저작권은 Lee.. 공감수 0 댓글수 0 2020. 6. 1.
LeetCode 876. Middle of the Linked List Problem: Given a non-empty, singly linked list with head node head, return a middle node of linked list. If there are two middle nodes, return the second middle node. Example 1: Input: [1,2,3,4,5] Output: Node 3 from this list (Serialization: [3,4,5]) The returned node has value 3. (The judge's serialization of this node is [3,4,5]). Note that we returned a ListNode object ans, such that: ans.va.. 공감수 0 댓글수 0 2020. 5. 31.
LeetCode 1290. Convert Binary Number in a Linked List to Integer Problem: Given head which is a reference node to a singly-linked list. The value of each node in the linked list is either 0 or 1. The linked list holds the binary representation of a number. Return the decimal value of the number in the linked list. Example 1: Input: head = [1,0,1] Output: 5 Explanation: (101) in base 2 = (5) in base 10 Example 2: Input: head = [0] Output: 0 Example 3: Input: h.. 공감수 0 댓글수 0 2020. 5. 31.
LeetCode 242. Delete Node in a Linked List Problem: Write a function to delete a node (except the tail) in a singly linked list, given only access to that node. Given linked list -- head = [4,5,1,9], which looks like following: Example 1: Input: head = [4,5,1,9], node = 5 Output: [4,1,9] Explanation: You are given the second node with value 5, the linked list should become 4 -> 1 -> 9 after calling your function. Example 2: Input: head =.. 공감수 0 댓글수 0 2020. 5. 31.

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