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| /* | |
| * Calculate the persistence of a number; | |
| * based on Numberphile video: | |
| * https://www.youtube.com/watch?v=Wim9WJeDTHQ | |
| */ | |
| function calculatePersistence (num) { | |
| let result = 1 | |
| while ((num = multiplyItems(getDigits(num))) > 0) | |
| result++ | |
| return result | |
| } | |
| function getDigits (num) { | |
| const result = [] | |
| while (num > 0) { | |
| const rem = num % 10 | |
| result.push(rem) | |
| num -= rem | |
| num /= 10 | |
| } | |
| return result | |
| } | |
| function multiplyItems (items) { | |
| return items.reduce((result, item) => | |
| (result * item), | |
| 1) | |
| } |
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