dfs проверка на двудольность

def dfs(h):
    global answ
    used[h] = 1
    for e in g[h]:
        if used[e] == 0:
            col[e] = col[h] ^ 1
            dfs(e)
        else:
            if col[e] == col[h]:
                answ = False


n, m = map(int, input().split())
g = [[] for i in range(n)]
for i in range(m):
    x, y = map(int, input().split())
    x -= 1
    y -= 1
    g[x].append(y)
    g[y].append(x)
used = [0] * n
col = [-1] * n
col[0] = 0
answ = True #граф двудольный
dfs(0)
print(answ)