import java.io.*;

//前缀和:改题目要求 求一串整数数列中l~r中的数的和
//可以提前算好前n项的和s[n],然后用s[n] - s[n - 1]

public class Main {
	static int n,m,l,r;
	static int N = 100010;
	static BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
	static BufferedWriter out = new BufferedWriter(new OutputStreamWriter(System.out));
	static int[] g = new int[N];
	public static void main(String[] args) throws IOException {
		String[] init = in.readLine().split(" ");
		n = Integer.parseInt(init[0]);
		m = Integer.parseInt(init[1]);
		
		init = in.readLine().split(" ");
		for(int i = 1;i <= n;i ++) {
			g[i] = g[i - 1] + Integer.parseInt(init[i - 1]);
		
		}
		while(m-- > 0) {
			init = in.readLine().split(" ");
			l = Integer.parseInt(init[0]);
			r = Integer.parseInt(init[1]);
			out.write((g[r] - g[l - 1]) + "\n");
		}
		in.close();
		out.flush();
	}
}

前缀和例题:二维前缀和

                   二维前缀和-2