[Leetcode]15. 3Sum

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Given an array nums of n integers, are there elements abc 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:
Given array nums = [-1, 0, 1, 2, -1, -4], A solution set is: [ [-1, 0, 1], [-1, -1, 2] ]
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[Leetcode]1498. Number of Subsequences That Satisfy the Given Sum Condition

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Given an array of integers nums and an integer target.
Return the number of non-empty subsequences of nums such that the sum of the minimum and maximum element on it is less or equal than target.
Since the answer may be too large, return it modulo 10^9 + 7.
Input: nums = [3,3,6,8], target = 10
Output: 6
Explanation: There are 6 subsequences that satisfy the condition. (nums can have repeated numbers).
[3] , [3] , [3,3], [3,6] , [3,6] , [3,3,6]
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[Leetcode]1497. Check If Array Pairs Are Divisible by k

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Given an array of integers arr of even length n and an integer k.
We want to divide the array into exactly n / 2 pairs such that the sum of each pair is divisible by k.
Return True If you can find a way to do that or False otherwise.
 
Example 1:
Input: arr = [1,2,3,4,5,10,6,7,8,9], k = 5 Output: true 
Explanation: Pairs are (1,9),(2,8),(3,7),(4,6) and (5,10).
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[Leetcode]957. Prison Cells After N Days

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There are 8 prison cells in a row, and each cell is either occupied or vacant.
Each day, whether the cell is occupied or vacant changes according to the following rules:
1. If a cell has two adjacent neighbors that are both occupied or both vacant, then the cell becomes occupied.
2. Otherwise, it becomes vacant.
(Note that because the prison is a row, the first and the last cells in the row can't have two adjacent neighbors.)
We describe the current state of the prison in the following way: cells[i] == 1 if the i-th cell is occupied, else cells[i] == 0.
Given the initial state of the prison, return the state of the prison after N days (and N such changes described above.)
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[Leetcode]212. Word Search II

Given a 2D board and a list of words from the dictionary, find all words in the board.
Each word must be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once in a word.
Example:
Input: board = 
[ ['o','a','a','n'], 
  ['e','t','a','e'], 
  ['i','h','k','r'], 
  ['i','f','l','v'] ] 
words = ["oath","pea","eat","rain"] 
Output: ["eat","oath"]
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