Given N and D, find if it is possible to make two sets from first N natural numbers such that the difference between the sum of 2 sets(individually) is D.
Input : 5 7 Output : yes Explanation: Keeping 1 and 3 in one set, and 2, 4 and 5 are in other set. Sum of set 1 = 4 Sum of set 2 = 11 So, the difference D = 7 Which is the required difference Input : 4 5 Output : no
Let s1 and s2 be the two sets.
Here we know that
sum(s1) + sum(s2) = N*(N+1)/2 and
sum(s1) – sum(s2) = D
Adding above 2 equations, we get
2*sum(s1) = N*(N+1)/2 + D
If sum(S1) and sum(S2) are integers, then only we can split the first N natural numbers into two sets. For that N*(N+1)/2 + D must be an even number.
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