README.md

1395. Count Number of Teams

There are n soldiers standing in a line. Each soldier is assigned a unique rating value.

You have to form a team of 3 soldiers amongst them under the following rules:

• Choose 3 soldiers with index (i, j, k) with rating (rating[i], rating[j], rating[k]).
• A team is valid if: (rating[i] < rating[j] < rating[k]) or (rating[i] > rating[j] > rating[k]) where (0 <= i < j < k < n).

Return the number of teams you can form given the conditions. (soldiers can be part of multiple teams).

Example 1:

Input: rating = [2,5,3,4,1]
Output: 3
Explanation: We can form three teams given the conditions. (2,3,4), (5,4,1), (5,3,1).

Example 2:

Input: rating = [2,1,3]
Output: 0
Explanation: We can't form any team given the conditions.

Example 3:

Input: rating = [1,2,3,4]
Output: 4

Constraints:

• n == rating.length
• 1 <= n <= 200
• 1 <= rating[i] <= 10^5

Solutions (Rust)

1. Solution

impl Solution {
    pub fn num_teams(rating: Vec<i32>) -> i32 {
        let mut ret = 0;

        for j in 1..(rating.len() - 1) {
            let ltl = rating[..j].iter().filter(|&&x| x < rating[j]).count();
            let gtl = j - ltl;
            let ltr = rating[j..].iter().filter(|&&x| x < rating[j]).count();
            let gtr = rating.len() - 1 - j - ltr;

            ret += ltl * gtr + ltr * gtl;
        }

        ret as i32
    }
}