README.md

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

Solutions (Rust)

1. Solution

use std::collections::HashMap;

impl Solution {
    pub fn unequal_triplets(nums: Vec<i32>) -> i32 {
        let mut count = HashMap::new();
        let mut ret = 0;

        for num in &nums {
            count.entry(num).and_modify(|c| *c += 1).or_insert(1);
        }

        let count = count.values().collect::<Vec<_>>();

        for i in 0..count.len() {
            for j in i + 1..count.len() {
                for k in j + 1..count.len() {
                    ret += count[i] * count[j] * count[k];
                }
            }
        }

        ret
    }
}