UVa - 10364 - Square

What is wrong with my solution for UVa - 10364 - Square ?

Algorithm : Divide the array of integers into 4 subsets, each of them having the same sum. I have used recursive backtracking to check all the possible combination. But for few cases it is showing WA.

Problem : https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&category=0&problem=1305&mosmsg=Submission+received+with+ID+23318406

Code : https://hastebin.com/qazanutagi.cpp