数据子序列

import java.util.Scanner;

public class 数列 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        while (input.hasNext()) {  
            int n = input.nextInt();
            int m = input.nextInt();
            int[] arr = new int[n];

            // 读取序列中的元素
            for (int i = 0; i < n; i++) {
                arr[i] = input.nextInt();
            }

            // 计算并输出最大子序列和
            System.out.println(maxSum(n, m, arr));
        }

        input.close();
    }

    public static int maxSum(int n, int m, int[] arr) {
        int maxSum = Integer.MIN_VALUE;


        for (int length = 1; length <= m; length++) {  //截取所需子序列长度
            int currentSum = 0;


            for (int i = 0; i < length; i++) {    //子序列求和
                currentSum += arr[i];
            }
            maxSum = Math.max(maxSum, currentSum);  //每次循环，将最大值付给maxSum


            for (int i = length; i < n; i++) {  //核心方法，窗口移动法；前面已经截取了子序列的长度，既定义了窗口，现在只需要将窗口按位移动至末尾即可，移动方法是获取一个新的数，放弃旧的数
即currentSum = currentSum + arr[i];向下移动获取新的数；currentSum = currentSum - arr[i-length]放弃旧的数，实现移动
                currentSum += arr[i] - arr[i - length];
                maxSum = Math.max(maxSum, currentSum);
            }
        }

        return maxSum;
    }
}