solution.cpp

class NumMatrix {
public:
    vector<vector<int>> dp;
    int row;
    int col;
    NumMatrix(vector<vector<int>> matrix) {
        row = matrix.size();
        col = row>0?matrix[0].size():0;
        dp = vector<vector<int>>(row+1, vector<int>(col+1,0));
        
        //
        for(int i=1;i<row+1;i++)
            for(int j=1;j<col+1;j++)
                dp[i][j] = matrix[i-1][j-1] + dp[i][j-1] + dp[i-1][j] - dp[i-1][j-1];
    }
    
    int sumRegion(int row1, int col1, int row2, int col2) {
        return dp[row2+1][col2+1] - dp[row2+1][col1] - dp[row1][col2+1] + dp[row1][col1];
    }
};

/**
 * Your NumMatrix object will be instantiated and called as such:
 * NumMatrix obj = new NumMatrix(matrix);
 * int param_1 = obj.sumRegion(row1,col1,row2,col2);
 */