308-range-sum-query-2d-mutable.cpp

class NumMatrix {
public:
    NumMatrix(vector<vector<int>>& matrix) : matrix(matrix) {
        this->rows = matrix.size();
        if (this->rows != 0) this->cols = matrix[0].size();
    }
    
    void update(int row, int col, int val) {
        matrix[row][col] = val;
    }
    
    int sumRegion(int row1, int col1, int row2, int col2) {
        int sum = 0;
        for (int i = row1; i <= row2; i++) {
            for (int j = col1; j <= col2; j++) {
                sum += matrix[i][j];
            }
        }
        return sum;
    }
    
private:
    vector<vector<int>>& matrix;
    int rows;
    int cols;
};

/**
 * Your NumMatrix object will be instantiated and called as such:
 * NumMatrix* obj = new NumMatrix(matrix);
 * obj->update(row,col,val);
 * int param_2 = obj->sumRegion(row1,col1,row2,col2);
 */