Решение задачи D городской олимпиады по информатике (г. Луганск, 2019 г.)

D.py

n, s = map(int, input().split())
def dfs(graph, start, visited=set()):
    if start not in visited:
        visited.add(start)
        for node in graph[start]:
            dfs(graph, node, visited)
        return visited
graph = dict()
for i in range(n):
    graph[i+1] = []
    layer = [int(i) for i in input().split()]
    for j in range(len(layer)):
        if layer[j] == 1:
            graph[i+1].append(j+1)
res = dfs(graph, s)
print(len(res)-1)