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Light.py

import sys

if len(sys.argv) < 2:
    print('Usage:\n$ python Lights.py 6575')
    sys.exit(0)
answer = int(sys.argv[1])
print(answer)

dp = [-1] * 10000
a = []

dp[0] = 0
a.append(0)

while a:
    b = a[0]
    a = a[1:]
    b1 = (b + 7) % 10000
    b2 = (b * 10) % 10000
    if dp[b1] == -1:
        a.append(b1)
        dp[b1] = b
    if dp[b2] == -1:
        a.append(b2)
        dp[b2] = b
    if b1 == answer or b2 == answer:
        break

print('===========')

i = answer
while True:
    print(i)
    i = dp[i]
    if i == 0:
        break