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LeetCode/Problems25

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 .. 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] 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.. 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.. 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.. 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.. 2020. 6. 11.

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