396. Rotate Function

Link: https://leetcode.cn/problems/rotate-function/

Question

difficulty: mid
adj diff: 4

You are given an integer array nums of length n.

Assume arrk to be an array obtained by rotating nums by k positions clock-wise. We define the rotation function F on nums as follow:

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

Return the maximum value of F(0), F(1), ..., F(n-1).

The test cases are generated so that the answer fits in a 32-bit integer.

Example 1:

Input: nums = [4,3,2,6]
Output: 26
Explanation:
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.

Example 2:

Input: nums = [100]
Output: 0

Constraints:

    n == nums.length
    1 <= n <= 105
    -100 <= nums[i] <= 100

Code

public int maxRotateFunction(int[] nums) {
    int n = nums.length;
    int arraySum = 0;
    int currentTotal = 0;
    for (int i = 0; i < n; i++) {
        arraySum += nums[i];
        currentTotal += i * nums[i];
    }
    int runningTotal = currentTotal;
    for (int i = 0; i < n; i++) {
        currentTotal += arraySum;
        currentTotal -= n * nums[n - 1 - i];
        runningTotal = Math.max(runningTotal, currentTotal);
    }
    return runningTotal;
}