DP [2D] -> (DDP2)

#include <iostream>
#include <vector>

using namespace std;

int main ()
{
    int n, m, q;
    cin>>n>>m;

    vector< vector<int> > mat (n, vector<int> (m) );
    vector< vector<int> > DP (n+1, vector<int> (m+1, 0) );

    for (int i=0; i<n; i++)
        for (int j=0; j<m; j++)
            cin>>mat[i][j];

    for (int i=1; i<=n; i++)
        for (int j=1; j<=m; j++)
            DP[i][j] = DP[i][j-1] + DP[i-1][j] + mat[i-1][j-1] - DP[i-1][j-1];

    cin>>q;
    int ax, ay, bx, by;

    for(int i=0; i<q; i++)
    {
        cin>>ax>>ay>>bx>>by;
        cout<< DP[bx+1][by+1] - DP[bx+1][ay] - DP[ax][by+1] + DP[ax][ay]<<endl;
    }
    return 0;
}