深度优先搜索DFS

def solve():
    graph = {____: [____, ____], ____: [____], ____: [____, ____], ____: [____]}
    visited = set()
    result = []
    
    def dfs(____):
        visited.add(____)
        result.append(str(____))
        for neighbor in graph[node]:
            if neighbor not in visited:
                dfs(____)
    
    dfs(____)
    print('____'.join(____))