SUBSET SUM problem in CODEX 2014

Problem link : http://www.codechef.com/CODX2014/problems/REN2013D

Please help me how to solve this problem and how this problem is different from standard subset sum problem(NP PROBLEM).The only way i was able to think is : check for each element from low to high that whether any subset whose sum is equal to it exists or not by using the recursive or dp approach.

Check Forbidden sum editorial in last long challenge.It’s idea is similar.

A brief solution outline can be found here http://discuss.codechef.com/questions/37595/codex-editorials-for-specopssubset-sum

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