# Adjacency list
first_graph = {
    1: [3, 20, 4, 5, 6],
    2: [20],
    3: [1, 20],
    20: [2, 3],
    4: [1],
    5: [1],
    6: [1]
}

# First exercise: go from 1, to 20, to 2
first_graph[first_graph[1][1]][0]

# pass visited by reference
def depth_first_search(graph: dict, start, visited=set(), traversal=list()):
    if start in visited:
        return

    visited.add(start)
    traversal.append(start)

    for x in graph[start]:
        depth_first_search(graph, x, visited, traversal)
    

visited = set()
traversal = list()
depth_first_search(first_graph, 1, visited, traversal)
print("Visited:", visited)
print("Traversal:", traversal)