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Kotlin-based LeetCode algorithm problem solutions, regularly updated
923\. 3Sum With Multiplicity
Medium
Given an integer array `arr`, and an integer `target`, return the number of tuples `i, j, k` such that `i < j < k` and `arr[i] + arr[j] + arr[k] == target`.
As the answer can be very large, return it **modulo** 109 + 7.
**Example 1:**
**Input:** arr = [1,1,2,2,3,3,4,4,5,5], target = 8
**Output:** 20
**Explanation:**
Enumerating by the values (arr[i], arr[j], arr[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.
**Example 2:**
**Input:** arr = [1,1,2,2,2,2], target = 5
**Output:** 12
**Explanation:**
arr[i] = 1, arr[j] = arr[k] = 2 occurs 12 times:
We choose one 1 from [1,1] in 2 ways,
and two 2s from [2,2,2,2] in 6 ways.
**Constraints:**
* `3 <= arr.length <= 3000`
* `0 <= arr[i] <= 100`
* `0 <= target <= 300`