_396.java

package com.fishercoder.solutions;

public class _396 {
    public static class Solution1 {
        /**
         * F(k) = 0 * Bk[0] + 1 * Bk[1] + ... + (n-1) * Bk[n-1]
         */
        public int maxRotateFunction(int[] A) {
            if (A == null || A.length == 0) {
                return 0;
            }
            int[] F = new int[A.length];
            int[] B = A;
            int max = Integer.MIN_VALUE;
            for (int i = 0; i < A.length; i++) {
                F[i] = compute(B);
                max = Math.max(max, F[i]);
                B = rotate(B);
            }
            return max;
        }

        private int compute(int[] b) {
            int sum = 0;
            for (int i = 0; i < b.length; i++) {
                sum += i * b[i];
            }
            return sum;
        }

        private int[] rotate(int[] a) {
            int first = a[0];
            for (int i = 1; i < a.length; i++) {
                a[i - 1] = a[i];
            }
            a[a.length - 1] = first;
            return a;
        }
    }

    public static class Solution2 {
        /**
         * Reference: https://discuss.leetcode.com/topic/58459/java-o-n-solution-with-explanation
         */
        public int maxRotateFunction(int[] A) {
            int allSum = 0;
            int len = A.length;
            int F = 0;
            for (int i = 0; i < len; i++) {
                F += i * A[i];
                allSum += A[i];
            }
            int max = F;
            for (int i = len - 1; i >= 1; i--) {
                F = F + allSum - len * A[i];
                max = Math.max(F, max);
            }
            return max;
        }
    }
}