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#advent of code 2020
#day 25
#I made a mistake by thinking that subject number is an unknow
#while in reality it actually is =7 as in puzzle description
def FindNumbers(pubkey):
S = 7;
L = 0;
v = 1;
while True:
L += 1;
v *= S;
v = v%20201227;
if v == pubkey:
return L; #gives loop number
PuzzleInput = open("25.in","r").read().split("\n");
cardkey = int(PuzzleInput[0]);
doorkey = int(PuzzleInput[1]);
#encryption key is the same
#whether we use loop of card + subject of door
#or loop of door + subject of card
encryption = 1;
for l in range(FindNumbers(cardkey)):
encryption *= doorkey;
encryption = encryption%20201227;
part1 = encryption;
print("part 1 =", part1);
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