Rotate Function
Desicription
Given an array of integers A and let n to be its length.
Assume Bk to be an array obtained by rotating the array A k positions clockwise, we define a “rotation function” F on A as follow:
F(k) = 0 * Bk[0] + 1 * Bk[1] + … + (n1) * Bk[n1].
Calculate the maximum value of F(0), F(1), …, F(n1).
Note:
n is guaranteed to be less than 105.
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 Example:
A = [4, 3, 2, 6]
F(0) = (0 * 4) + (1 * 3) + (2 * 2) + (3 * 6) = 0 + 3 + 4 + 18 = 25 F(1) = (0 * 6) + (1 * 4) + (2 * 3) + (3 * 2) = 0 + 4 + 6 + 6 = 16 F(2) = (0 * 2) + (1 * 6) + (2 * 4) + (3 * 3) = 0 + 6 + 8 + 9 = 23 F(3) = (0 * 3) + (1 * 2) + (2 * 6) + (3 * 4) = 0 + 2 + 12 + 12 = 26

So the maximum value of F(0), F(1), F(2), F(3) is F(3) = 26.
Solution
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 class Solution { public: long long maxRotateFunction(const std::vector<int>& A) { long long res = LONG_LONG_MIN; for(int i = 0; i < A.size(); i++) { long long sum = 0; for(int index = i, count = 0; count < A.size(); index = (index + 1) % A.size(), count++) { sum += A[index] * count; } res = std::max(res, sum); } return A.empty() ? 0 : res; } };
