백준 2606번(python)

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import sys

input = sys.stdin.readline

N = int(input())
conn_num = int(input())

networks = [[0] * (N + 1) for _ in range(N+1)]

for _ in range(conn_num):
    a, b = map(int, input().split())
    networks[a][b] = 1; networks[b][a] = 1
    
def dfs(current_node, networks, foot_print):
    foot_print += [current_node]
    
    for search_node in range(len(networks[current_node])):
        if networks[current_node][search_node] and search_node not in foot_print:
            foot_print = dfs(search_node, networks, foot_print)
            
    return foot_print

result = dfs(1, networks, [])

print(len(result) - 1)