算法基础

算法：前缀和

#include <bits/stdc++.h>

using namespace std;
const int N = 1e5 + 10;

int a[N], s[N];  //s[N]前缀和数组 s[i] = a[1] + a[2] + a[3] + ...+ a[i]
int main(){
	int n, m;
	cin >> n >> m;
	for(int i = 1; i <= n; i++){
		cin >> a[i];
	}
	
	for(int i = 1; i <= n; i++){  //前缀和公式:s[n] = s[n-1] + a[n]
		s[i] = s[i - 1] + a[i];
	}
	
	while(m--){
		int l, r;
		cin >> l >> r;
		
		cout << s[r] - s[l - 1] << endl;  //[l~r]的前缀和公式：s[r] - s[l-1]
	}
	
	
	return 0;
}