def __init__(self, matrix):
        """
        initialize your data structure here.
        :type matrix: List[List[int]]
        """
        if matrix is None or len(matrix) == 0:
            return
        height, width = len(matrix), len(matrix[0])
        self.dp = [[0]* (width + 1) for i in range(height + 1)]
        for i in range(height):
            for j in range(width):
                self.dp[i + 1][j + 1] = self.dp[i + 1][j] + \
                                        self.dp[i][j + 1] + matrix[i][j] - self.dp[i][j]

        initialize your data structure here.
        :type matrix: List[List[int]]
        
python/304_Range_Sum_Query_2D_Immutable.py