## Leetcode - 3Sum With Multiplicity

https://leetcode.com/problems/3sum-with-multiplicity/

Given an integer array `A`, and an integer `target`, return the number of tuples `i, j, k`  such that `i < j < k` and `A[i] + A[j] + A[k] == target`.

As the answer can be very large, return it modulo `10^9 + 7`.

Example 1:

```Input: A = [1,1,2,2,3,3,4,4,5,5], target = 8
Output: 20
Explanation:
Enumerating by the values (A[i], A[j], A[k]):
(1, 2, 5) occurs 8 times;
(1, 3, 4) occurs 8 times;
(2, 2, 4) occurs 2 times;
(2, 3, 3) occurs 2 times.
```

## Leetcode - 3Sum

https://leetcode.com/problems/3sum/

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:

```Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
[-1, 0, 1],
[-1, -1, 2]
]
```

## Leetcode - 3Sum Smaller

https://leetcode.com/problems/3sum-smaller/

Given an array of n integers nums and a target, find the number of index triplets `i, j, k` with `0 <= i < j < k < n` that satisfy the condition `nums[i] + nums[j] + nums[k] < target`.

Example:

```Input: nums = `[-2,0,1,3]`, and target = 2
Output: 2
Explanation: Because there are two triplets which sums are less than 2:
[-2,0,1]
[-2,0,3]
```

## Leetcode - 3sum-closest

Given an array `nums` of n integers and an integer `target`, find three integers in `nums` such that the sum is closest to `target`. Return the sum of the three integers. You may assume that each input would have exactly one solution.

Example:

```Given array nums = [-1, 2, 1, -4], and target = 1.

The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).
```