124 나라의 숫자

from collections import deque
data=["1", "2", "4"]
def bfs(n):
    queue = deque()
    r_num=0
    queue.append(("", r_num))
    while queue:
        string, num = queue.popleft()
        if num==n:
            return string
        else:
            for i in range(3):
                r_num+=1
                queue.append((string+data[i], r_num))
def solution(n):
    answer = ''
    answer = bfs(n)
    return answer