题解 | 【模板】前缀和

import java.util.*;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNext()) { // 注意 while 处理多个 case
            int n = in.nextInt();
            int m = in.nextInt();
            in.nextLine();
            int[] arr = new int[n];
            for (int i=0; i<n; i++) {
                arr[i] = in.nextInt();
            }

            // 先计算 preifx
            long[] prefix = new long[n + 1];
            for (int i=1; i<=n; i++) {
                prefix[i] = prefix[i-1] + arr[i-1];
            }
            while (m-- > 0) {
                int left = in.nextInt();
                int right = in.nextInt();
                //System.out.println("left:" + left + " right:" + right);
                long res = process(prefix, left, right);
                System.out.println(res);
            }

        }
    }


    private static long process(long[] prefix, int l, int r) {
        return prefix[r] - prefix[l-1];

    }
}