53 lines
1.0 KiB
Python
53 lines
1.0 KiB
Python
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class Step:
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l = []
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d = {}
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limit = 0
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def __init__(self, num):
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self.limit = 5 * num
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self.l = [0] * self.limit
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self.l[0] = 1
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def __getitem__(self, key):
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if self.limit > key:
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return self.l[key]
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else:
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return self.d.setdefault(key, 0)
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def __setitem__(self, key, value):
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if self.limit > key:
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self.l[key] = value
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else:
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self.d[key] = value
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def collatz_step(x, path):
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global steps
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if steps[x - 1]:
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foot = steps[x - 1] + 1
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while path:
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steps[path.pop() - 1] = foot
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foot += 1
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return
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else:
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path.append(x)
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if x % 2:
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collatz_step(3 * x + 1, path)
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else:
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collatz_step(x // 2, path)
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def collatz_max(num):
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global steps
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for x in range(1, num + 1):
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if steps[x - 1]:
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continue
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collatz_step(x, [])
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return steps.l.index(max(steps.l[:num])) + 1
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limit = 1000000
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steps = Step(limit)
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print(collatz_max(limit))
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