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41 lines
No EOL
1 KiB
Ruby
41 lines
No EOL
1 KiB
Ruby
#Problem 14: https://projecteuler.net/problem=14
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#Problem Statement:
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#The following iterative sequence is defined for the set of positive integers:
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#
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# n → n/2 (n is even)
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# n → 3n + 1 (n is odd)
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#
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#Using the rule above and starting with 13, we generate the following sequence:
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#
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# 13 → 40 → 20 → 10 → 5 → 16 → 8 → 4 → 2 → 1
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#
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#It can be seen that this sequence (starting at 13 and finishing at 1) contains
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#10 terms. Although it has not been proved yet (Collatz Problem), it is thought
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#that all starting numbers finish at 1.
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#Which starting number, under one million, produces the longest chain?
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def solution()
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index_best_result = 0
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for num in 2..1000000
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index_candidate = 0
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n = num
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while n > 1
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if n%2 == 0
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n = n / 2
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else
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n = (3*n) + 1
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end
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index_candidate +=1
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end
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if index_best_result < index_candidate
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index_best_result = index_candidate
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value = num
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end
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end
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result = value
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end
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answer = solution()
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p answer |