304. Range Sum Query 2D - Immutable

class NumMatrix {

    int[][] matrix;
    public NumMatrix(int[][] matrix) {
        for(int i=0;i<matrix.length;i++){
            for(int j=1;j<matrix[0].length;j++){
                matrix[i][j] += matrix[i][j-1];
            }
        }
        
        for(int i=1;i<matrix.length;i++){
            for(int j=0;j<matrix[0].length;j++){
                matrix[i][j] += matrix[i-1][j];
            }
        }
        
        this.matrix = matrix;
    }
    
    public int sumRegion(int row1, int col1, int row2, int col2) {
        int total = matrix[row2][col2];
        int extra = (col1!=0?matrix[row2][col1-1]:0) + (row1!=0?matrix[row1-1][col2]:0) - ((row1!=0 && col1!=0)?matrix[row1-1][col1-1]:0);
        return total - extra;
    }
}

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