Acwing_795前缀和 【一维前缀和】 

题目：

代码： 

#include <bits/stdc++.h>
#define int long long
#define INF 0X3f3f3f3f
#define endl '\n'
using namespace std;
const int N = 100010;
int arr[N];

int n,m;
int l,r;
signed main(){
	
	std::ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	cin>>n>>m;
	int sum[N];
	for(int i = 1; i <= n; i++){
		cin>>arr[i];
		sum[i]= sum[i-1] + arr[i];
	}
	while(m--){
		cin>>l>>r;
		cout<<sum[r]- sum[l-1]<<endl;
	}
	return 0;
}

【模板】二维前缀和 

例题

#include <bits/stdc++.h>
#define int long long
#define endl '\n'
#define INF 0x3f3f3f3f3f
using namespace std;

const int N = 10010;
int arr[N][N],pre[N][N];
int n,c;

signed main(){

	std::ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int n,m;
	long long k;
	cin>>n>>m>>k;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            cin>>arr[i][j];
            pre[i][j]=pre[i-1][j]+pre[i][j-1]-pre[i-1][j-1]+arr[i][j];
        }
 
    }
 
    while(k--){
		int x1,y1,x2,y2;
		cin>>x1>>y1>>x2>>y2;
		cout<<pre[x2][y2]-pre[x1-1][y2]-pre[x2][y1-1]+pre[x1-1][y1-1]<<endl;
	}

	return 0;
}