Given an array of integers `nums` and an integer `target`, return the number of index triplets such that the sum of the three numbers is less than `target`.
nums = array of integers, target = integer target sum
number of triplets with sum less than target
Example 1:
Input:
nums = [-2,0,1,3] target = 2
Output:
2
Explanation:
Triplets are [-2,0,1] and [-2,0,3] which sum < 2.
Example 2:
Input:
nums = [3,1,0,-2] target = 4
Output:
3
Explanation:
Triplets are [-2,0,1], [-2,0,3], [-2,1,3] sum < 4.
Example 3:
Input:
nums = [1,1,1,1] target = 5
Output:
4
Explanation:
All 4 combinations of 3 ones sum 3 (<5).