最小平均差

/*
 * 思路：
 * 1. 使用流计算 nums 的总和。
 * 2. 通过流来遍历每个下标，计算前 i + 1 个元素和后 n - i - 1 个元素的平均值，然后计算绝对差。
 * 3. 通过流操作找到最小绝对差的下标。
 */
import java.util.stream.IntStream;
public int minimumAverageDifference(int[] nums) {
    int n = nums.length;
    long totalSum = IntStream.of(nums).asLongStream().sum();
    long[] preSum = new long[n];
    preSum[0] = nums[0];
    for (int i = 1; i < n; i++) {
        preSum[i] = preSum[i - 1] + nums[i];
    }
    return IntStream.range(0, n).reduce((i, j) -> {
        long frontAvg = preSum[i] / (i + 1);
        long backAvg = (n - i - 1 == 0) ? 0 : (totalSum - preSum[i]) / (n - i - 1);
        long diff1 = Math.abs(frontAvg - backAvg);
        long frontAvg2 = preSum[j] / (j + 1);
        long backAvg2 = (n - j - 1 == 0) ? 0 : (totalSum - preSum[j]) / (n - j - 1);
        long diff2 = Math.abs(frontAvg2 - backAvg2);
        return diff1 <= diff2 ? i : j;
    }).orElse(0);
}