leetcode-162周赛-1252-奇数值单元格数目

　题目描述：

自己的提交：

class Solution:
    def oddCells(self, n: int, m: int, indices: List[List[int]]) -> int:
        nums = [[0] * m for _ in range(n)]
        for i,j in indices:
            for k in range(m):
                nums[i][k] += 1
            for k in range(n):
                nums[k][j] += 1
        res = 0
        for i in range(n):
            for j in range(m):
                if nums[i][j] % 2 == 1:
                    res += 1
        return res

优化：

class Solution:
    def oddCells(self, n: int, m: int, indices: List[List[int]]) -> int:
        nums = [[0] * m for _ in range(n)]
        for i,j in indices:
            for k in range(m):
                nums[i][k] ^= 1
            for k in range(n):
                nums[k][j] ^= 1
        return sum(sum(row) for row in nums)

方法二：O(N)

class Solution:
    def oddCells(self, n: int, m: int, indices: List[List[int]]) -> int:
        a = [0]*n
        b = [0]*m
        for x, y in indices:
            a[x] ^= 1
            b[y] ^= 1
        return a.count(0)*b.count(1) + a.count(1)*b.count(0)