Write a Program to Find Number of Unequal Triplets in Array

# 2475. Number of Unequal Triplets in Array

You are given a 0-indexed array of positive integers nums. Find the number of triplets (i, j, k) that meet the following conditions:

0 <= i < j < k < nums.length nums[i], nums[j], and nums[k] are pairwise distinct. In other words, nums[i] != nums[j], nums[i] != nums[k], and nums[j] != nums[k]. Return the number of triplets that meet the conditions.

### Example 1:
“`
Input: nums = [4,4,2,4,3]
Output: 3
Explanation: The following triplets meet the conditions:
– (0, 2, 4) because 4 != 2 != 3
– (1, 2, 4) because 4 != 2 != 3
– (2, 3, 4) because 2 != 4 != 3
Since there are 3 triplets, we return 3.
Note that (2, 0, 4) is not a valid triplet because 2 > 0.
“`

### Example 2:
```
Input: nums = [1,1,1,1,1]
Output: 0
Explanation: No triplets meet the conditions so we return 0.
 ```

Constraints:
```
3 <= nums.length <= 100
1 <= nums[i] <= 1000
```

/**
 * @param {number[]} nums
 * @return {number}
 */
 var unequalTriplets = function(nums) {
    const hashMap = {};
    for(const item of nums) {
        hashMap[item] = hashMap[item] ? hashMap[item] + 1 : 1;
    }
 
    let left = 0, right = nums.length, out = 0;
    for (const freq of Object.values(hashMap)) {
        right -= freq;
        out += left * freq * right;
        left += freq;
    }
    return out;
 };