图论题1

一个很经典的图论题，写法如下

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first=set()
second=set()
directions=[[0,1],[1,0],[0,-1],[-1,0]]
def dfs(i,j,graph,vis,side):
    if vis[i][j]:
        return
    vis[i][j]=True
    side.add((i,j))
    for dir in directions:
        new_x=i+dir[0]
        new_y=j+dir[1]
        if (0<=new_x<len(graph)
                and 0<=new_y<len(graph[0])
                and graph[i][j]<=graph[new_x][new_y]):
            dfs(new_x,new_y,graph,vis,side)
n,m=map(int,input().split())
graph=[]
for i in range(n):
    a=list(map(int,input().split()))
    graph.append(a)
vis=[[False]*n for _ in range(m)]
for i in range(n):
    dfs(i,0,graph,vis,first)
for j in range(m):
    dfs(0,j,graph,vis,first)
vis=[[False]*n for _ in range(m)]
for i in range(n):
    dfs(i,m-1,graph,vis,second)
for j in range(m):
    dfs(n-1,j,graph,vis,second)
res=first&second
for x,y in res:
    print(f"{x} {y}")