[leetcode]396. Rotate Function

题目链接:https://leetcode.com/problems/rotate-function/

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 clock-wise,
we define a "rotation function" 

F

 on 

A

 as
follow:

F(k) = 0 * Bk[0]
+ 1 * Bk[1] + ... + (n-1) * Bk[n-1]

.

Calculate the maximum value of 

F(0), F(1), ..., F(n-1)

.

Note:
n is guaranteed to be less than 105.

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.

class Solution{
public:
int maxRotateFunction(vector<int>& A)
{
if(A.size()==0||A.size()==1)
return 0;
int num=0;
int rotateValue=0;
for(int i=0;i<A.size();i++)
{
num+=A[i];
rotateValue+=i*A[i];
}
int maxValue=rotateValue;
for(int i=(int)A.size()-1;i>=1;i--)
{
rotateValue=rotateValue-((int)A.size()-1)*A[i]+(num-A[i]);
maxValue=max(maxValue,rotateValue);

}
return maxValue;
}
};