#1395
Count Number of Teams
medium · verified · 70.2% accepted · 3,448 likes · top 79%
array · dynamic programming · binary indexed tree · segment tree
Description
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
Solution