编辑代码

import java.util.Arrays;

public class Solution {

    public static void main(String[] args) {
        int[] x = {10, 20, 30, 40, 50, 60, 70, 80, 90};
        int k = 3;
        int index = findClosestSubsequenceIndex(x, k);
        System.out.println("The index is: " + index);
    }

    public static int findClosestSubsequenceIndex(int[] x, int k) {
        // Step 1: Calculate the median of the array.
        int[] sortedX = Arrays.copyOf(x, x.length);
        Arrays.sort(sortedX);
        int median;
        int n = x.length;
        if (n % 2 == 0) {
            // For an even number of elements, take the lower middle value.
            median = sortedX[n / 2 - 1];
        } else {
            // For an odd number of elements, take the middle value.
            median = sortedX[n / 2];
        }

        int bestIndex = -1;
        int minDiff = Integer.MAX_VALUE;

        // Step 2 and 3: Iterate over all possible subsequences of length k.
        for (int i = 0; i <= x.length - k; i++) {
            int alternatingSum = 0;
            boolean add = true;
            for (int j = i; j < i + k; j++) {
                alternatingSum += add ? x[j] : -x[j];
                add = !add; // Alternate between adding and subtracting
            }

            // Calculate the absolute difference from the median.
            int diff = Math.abs(alternatingSum - median);

            // Update index if this subsequence is closer to the median or equal but larger index.
            if (diff < minDiff || (diff == minDiff && i > bestIndex)) {
                minDiff = diff;
                bestIndex = i;
            }
        }

        return bestIndex;
    }
}