【力扣100】994.腐烂的橘子tangerine

python 复制代码

class Solution:
    def orangesRotting(self, grid: List[List[int]]) -> int:
        # 思路是bfs，使用队列控制腐烂橘子的进出，然后在while循环末位对结果进行控制
        if not grid or len(grid)==0:
            return -1
            
        def check_zeros(array):
            for row in array:
                for elem in row:
                    if elem != 0:
                        return False
            return True
        myflag=check_zeros(grid)
        if myflag:
            return 0

        que=collections.deque()
        result=0
        row=len(grid)
        col=len(grid[0])
        for i in range(row):
            for j in range(col):
                if grid[i][j]==2:
                    que.append([i,j])
                if (
                    (i-1<0 or grid[i-1][j]==0) and 
                    (j-1<0 or grid[i][j-1]==0) and 
                    (i+1>=row or grid[i+1][j]==0) and 
                    (j+1>=col or grid[i][j+1]==0) and 
                    grid[i][j]==1
                    ):
                    return -1
        if not que:
            return -1
        while que:
            size=len(que)
            result+=1
            while size:
                cur=que.popleft()
                x=cur[0]
                y=cur[1]
                if x-1>=0 and grid[x-1][y]==1:
                    que.append([x-1,y])
                    grid[x-1][y]=2
                if y-1>=0 and grid[x][y-1]==1:
                    que.append([x,y-1])
                    grid[x][y-1]=2
                if x+1<row and grid[x+1][y]==1:
                    que.append([x+1,y])
                    grid[x+1][y]=2
                if y+1<col and grid[x][y+1]==1:
                    que.append([x,y+1])
                    grid[x][y+1]=2
                size-=1
        return result-1

思路：

bfs，使用队列维护，使用reslut控制结果
我自己写的这个打了很多补丁，然后还是有很多条件没有考虑到，但大体上bfs的思路是正确的

官方题解（也是bfs，而且多源我也考虑到了）：

python 复制代码

class Solution:
    def orangesRotting(self, grid: List[List[int]]) -> int:
        R, C = len(grid), len(grid[0])

        # queue - all starting cells with rotting oranges
        queue = collections.deque()
        for r, row in enumerate(grid):
            for c, val in enumerate(row):
                if val == 2:
                    queue.append((r, c, 0))

        def neighbors(r, c) -> (int, int):
            for nr, nc in ((r - 1, c), (r, c - 1), (r + 1, c), (r, c + 1)):
                if 0 <= nr < R and 0 <= nc < C:
                    yield nr, nc

        d = 0
        while queue:
            r, c, d = queue.popleft()
            for nr, nc in neighbors(r, c):
                if grid[nr][nc] == 1:
                    grid[nr][nc] = 2
                    queue.append((nr, nc, d + 1))

        if any(1 in row for row in grid):
            return -1
        return d