一维和二维前缀和

一维：

 1 #include <iostream>
 2 #include <vector>
 3 
 4 using namespace std;
 5 
 6 vector<int> arr(1e6+10,0);
 7 vector<long long> sum(1e6+10,0);
 8 
 9 int main(){
10     int n, m, l, r;
11     cin >> n >> m;
12     for(int i = 1;i <= n;++i)
13         cin >> arr[i];
14         
15     sum[0] = 0;    
16     for(int i = 1;i <= n;++i)
17         sum[i] = sum[i-1] + arr[i]; 
18     
19         
20     for(int i = 0;i < m;++i){
21         cin >> l >> r;
22         cout << sum[r] - sum[l-1] << endl;
23     }
24     
25     
26 }

code

二维

 1 #include <iostream>
 2 
 3 using namespace std;
 4 
 5 const int N = 1000+10;
 6 int arr[N][N] = {0}, s[N][N] = {0};
 7 int n, m, q; 
 8 
 9 int main(){
10     cin >> n >> m >> q;
11     for(int i = 1;i <= n;++i)
12         for(int j = 1;j <= m;++j)
13             cin >> arr[i][j];
14     
15     for(int i = 1;i <= n;++i)
16         for(int j = 1;j <= m;++j)
17             s[i][j] = s[i-1][j] + s[i][j-1] - s[i-1][j-1] + arr[i][j];//公式
18             
19     int x1,y1, x2,y2;//左上角和右下角下标
20     for(int i = 0;i < q;++i){
21         cin >> x1 >> y1 >> x2 >> y2;
22         cout << s[x2][y2] - s[x1-1][y2] - s[x2][y1-1] + s[x1-1][y1-1] << endl;
23     }
24         
25     return 0;
26 }

Code