[二维前缀和]304. 二维区域和检索 - 矩阵不可变

先做个垃圾出来………2025-08-25 18:01

Leetcode-304.二维区域和检索-矩阵不可变_哔哩哔哩_bilibili

python 复制代码

class NumMatrix:

    def __init__(self, matrix: List[List[int]]):
        m, n = len(matrix),len(matrix[0])
        s = [[0]*(n+1) for _ in range(m+1)]
        for i,row in enumerate(matrix):
            for j,x in enumerate(row):
                s[i+1][j+1] = s[i+1][j] + s[i][j+1] -s[i][j]+x
        self.s = s

    def sumRegion(self, row1: int, col1: int, row2: int, col2: int) -> int:
        return self.s[row2+1][col2+1] - self.s[row2+1][col1]-self.s[row1][col2+1]+self.s[row1][col1]

        


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