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#
# Solution to Project Euler problem 14
# Copyright (c) Project Nayuki. All rights reserved.
#
# https://www.nayuki.io/page/project-euler-solutions
# https://github.com/nayuki/Project-Euler-solutions
#
import eulerlib, sys
if sys.version_info.major == 2:
range = xrange
# We compute the Collatz chain length for every integer in the range according to the iteration rule.
# Also, we cache the Collatz value for all integer arguments to speed up the computation.
def compute():
sys.setrecursionlimit(3000)
ans = max(range(1, 1000000), key=collatz_chain_length)
return str(ans)
@eulerlib.memoize
def collatz_chain_length(x):
if x == 1:
return 1
if x % 2 == 0:
y = x // 2
else:
y = x * 3 + 1
return collatz_chain_length(y) + 1
if __name__ == "__main__":
print(compute())