tj,前缀和即可

#include<bits/stdc++.h>
#include<vector>
using namespace std;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int n, m;
cin >> n >> m;
auto w = vector<long long>(n+1, 0);
auto prefix = vector<long long>(n+1, 0);
for(auto i = 1; i <= n; i++){
cin >> w[i];
prefix[i] = prefix[i-1] + w[i];
}
for(auto i = 0; i < m; i++){
int l, r;
cin >> l >> r;
cout << prefix[r] - prefix[i-1] << endl;
}
return 0;
}