Part of course:
Four Sum (ZCO 2017: India)
Given an array of N integers and an integer T, find all possible combinations of indices i, j, k, l such that i < j < k < l and S[i] + S[j] + S[k] + S[l] is equal to T where S is the array of integers
Constraints: N <= 5000, T <= 10^6
Zonal Computing Olympiad is round 1 out of 3 for the selection of the Indian IOI team.