图的深度优先搜索DFS

def solve():
    graph = {____: [____, ____], ____: [____, ____], ____: [____], ____: [____]}
    visited = []
    def dfs(____):
        if node in visited:
            return
        visited.append(____)
        for neighbor in graph[node]:
            dfs(____)
    dfs(____)
    print('____'.join(map(____)))