can anyone optimize this code.giving tle.i want to do it using stl only
answer-
question-http://www.spoj.com/problems/SUMFOUR/
As you are trying to generate all the combination of summation and looping it through it is causing the TLE , your approach is correct but you need to be little bit smarter in searching the element in the multiset which will give the AC 
Just remember in worst case the summation of A and B set or C and D set can give 4000 * 4000 elements which will be equal to 16 * 10 ^ 6 and then looping through the both may lead to to way beyond 10^9 loop …I have given enough hint you to go ahead think more remember smarted search