Wrong :c

matrix_3 = [[0, 1, 1, 0, 0, 0, 0],  # 3 компоненты связности
     [1, 0, 1, 0, 0, 0, 0],
     [1, 1, 0, 1, 0, 0, 0],
     [0, 0, 1, 0, 0, 0, 0],
     [0, 0, 0, 0, 0, 1, 0],
     [0, 0, 0, 0, 1, 0, 0],
     [0, 0, 0, 0, 0, 0, 0]]

matrix_2 = [[0, 1, 0], #2 компоненты связности
            [1, 0, 0],
            [0, 0, 0]]

def answer():
    visited = set()
    k = 0

    def dfs(node):   # start from 0
        visited.add(node)
        for v in range(len(matrix_3)):
            if matrix_3[node][v] == 1 and v not in visited:
               dfs(v)
        for v in visited:
            if v not in visited:
                k+=1

def main():
    vertexes = answer(0) #???
    print(vertexes)

if __name__ == '__main__':
    main()