1512. Number of Good Pairs

Given an array of integers nums.
A pair (i,j) is called good if nums[i] == nums[j] and i < j.
Return the number of good pairs.

• Example 1:
  Input: nums = [1,2,3,1,1,3]
  Output: 4
  Explanation: There are 4 good pairs (0,3), (0,4), (3,4), (2,5) 0-indexed.

• Example 2:
  Input: nums = [1,1,1,1]
  Output: 6
  Explanation: Each pair in the array are good.

• Example 3:
  Input: nums = [1,2,3]
  Output: 0

var numIdenticalPairs = function(nums) {
  let matchNum = 0;
  const iterator = nums.entries();
  let goalValue;
  for(let idx = 0; idx < nums.length; idx++) 
  {
      goalValue = iterator.next().value;
      let matchArr = nums.map((i, idx) => goalValue[1] === i && goalValue[0] < idx);
      matchArr.forEach(i => {
        if(i) matchNum++;
      });
  }
  return matchNum;
};