Qingdao Race Training (number theory)

Qingdao Race Training A-fantasy of a summation LightOJ-1213 time: October 5 23 o'clock 30

Https://cn.vjudge.net/contest/258301#problem
The problem, test instructions gives is a K-cycle, each loop I weighs 1 to n, the loop body is res = (res + A[I1] + A[i2] + ... + a[ik])% MOD; The value of the last res.

Analysis: Combinatorial math + fast Power

Solution: For each a[i] is the same,
So we figure out the total a[i] The number of occurrences/n to know the number of occurrences
The total number of times is (n^k)K, so each occurrence (n^ (k-1))K
So the answer is sum(n^ (k-1))K%mod, which is finally solved with a fast power.

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Qingdao Race Training (number theory)