Solution.py

class Solution:
    def minimumOperations(self, grid: List[List[int]]) -> int:
        def find(i: int) -> int:
            for j in g[i]:
                if j not in vis:
                    vis.add(j)
                    if match[j] == -1 or find(match[j]):
                        match[j] = i
                        return 1
            return 0

        g = defaultdict(list)
        m, n = len(grid), len(grid[0])
        for i, row in enumerate(grid):
            for j, v in enumerate(row):
                if (i + j) % 2 and v:
                    x = i * n + j
                    if i < m - 1 and grid[i + 1][j]:
                        g[x].append(x + n)
                    if i and grid[i - 1][j]:
                        g[x].append(x - n)
                    if j < n - 1 and grid[i][j + 1]:
                        g[x].append(x + 1)
                    if j and grid[i][j - 1]:
                        g[x].append(x - 1)

        match = [-1] * (m * n)
        ans = 0
        for i in g.keys():
            vis = set()
            ans += find(i)
        return ans