一夜无解，痛苦，遂拜倒于灵神门下，妄做狂徒也！

. - 力扣（LeetCode）

灵神秒解如下：

class NumMatrix:
    #二维初始矩阵
    def __init__(self, matrix: List[List[int]]):
       m=len(matrix)
       n=len(matrix[0])
       #扩充一下，防止数组越界
       sum=[[0]*(n+1) for _ in range(m+1)]
       for i in range(m):
           for j in range(n):
             sum[i+1][j+1]=sum[i+1][j]+sum[i][j+1]-sum[i][j]+matrix[i][j]
       self.sum=sum

    #子矩阵计算和
    def sumRegion(self, row1: int, col1: int, row2: int, col2: int) -> int:
       return self.sum[row2+1][col2+1]-self.sum[row2+1][col1]-self.sum[row1][col2+1]+self.sum[row1][col1]