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LeetCode 396. 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 = 25F(1) = (0 * 6) + (1 * 4) + (2 * 3) + (3 * 2) = 0 + 4 + 6 + 6 = 16F(2) = (0 * 2) + (1 * 6) + (2 * 4) + (3 * 3) = 0 + 6 + 8 + 9 = 23F(3) = (0 * 3) + (1 * 2) + (2 * 6) + (3 * 4) = 0 + 2 + 12 + 12 = 26So the maximum value of F(0), F(1), F(2), F(3) is F(3) = 26.
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这个题目的关键是我们不能每次都要全部乘一遍,我们算完第一次后,就可以利用第一次的结果,来计算下一个移动后的结果
计算公式为:temp = temp - (sum - A[i]) + A[i] * (A.size() - 1);temp为上一次的结果,sum为数组的和
class Solution {public: int maxRotateFunction(vector<int>& A) { long long result = 0; long long sum = 0; long long temp = 0; for (int i = 0;i < A.size();++i) { result += A[i] * i; sum += A[i]; } temp = result; for (int i = 0;i < A.size();++i) { temp = temp - (sum - A[i]) + A[i] * (A.size() - 1); if (temp > result) result = temp; } return result; }};
LeetCode 396. Rotate Function
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