Cut Off Trees for Golf Event — LeetCode 675 Python Solution

class Solution:
    def cutOffTree(self, forest: List[List[int]]) -> int:
        def f(i, j, x, y):
            return abs(i - x) + abs(j - y)

        def bfs(i, j, x, y):
            q = [(f(i, j, x, y), i, j)]
            dist = {i * n + j: 0}
            while q:
                _, i, j = heappop(q)
                step = dist[i * n + j]
                if (i, j) == (x, y):
                    return step
                for a, b in [[0, -1], [0, 1], [-1, 0], [1, 0]]:
                    c, d = i + a, j + b
                    if 0 <= c < m and 0 <= d < n and forest[c][d] > 0:
                        if c * n + d not in dist or dist[c * n + d] > step + 1:
                            dist[c * n + d] = step + 1
                            heappush(q, (dist[c * n + d] + f(c, d, x, y), c, d))
            return -1

        m, n = len(forest), len(forest[0])
        trees = [
            (forest[i][j], i, j) for i in range(m) for j in range(n) if forest[i][j] > 1
        ]
        trees.sort()
        i = j = 0
        ans = 0
        for _, x, y in trees:
            t = bfs(i, j, x, y)
            if t == -1:
                return -1
            ans += t
            i, j = x, y
        return ans