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February 28, 2021 17:27
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| /** | |
| Eloquent Javascript CH003 | |
| Consider this puzzle: by starting from the number 1 and repeatedly either | |
| adding 5 or multiplying by 3, an infinite set of numbers can be produced. | |
| How would you write a function that, given a number, tries to find | |
| a sequence of such additions and multiplications that produces that number? | |
| */ | |
| function findSolution(target) { | |
| function find(current, history) { | |
| if (current == target) { | |
| return history; | |
| } else if (current > target) { | |
| return null; | |
| } else { | |
| return find(current + 5, `(${history} + 5)`) || | |
| find(current * 3, `(${history} * 3)`); | |
| } | |
| } | |
| return find(1, "1"); | |
| } | |
| console.log(findSolution(24)); | |
| // → (((1 * 3) + 5) * 3) | |
| // VISUAL | |
| /** | |
| find(1, "1") | |
| find(6, "(1 + 5)") | |
| find(11, "((1 + 5) + 5)") | |
| find(16, "(((1 + 5) + 5) + 5)") | |
| too big | |
| find(33, "(((1 + 5) + 5) * 3)") | |
| too big | |
| find(18, "((1 + 5) * 3)") | |
| too big | |
| find(3, "(1 * 3)") | |
| find(8, "((1 * 3) + 5)") | |
| find(13, "(((1 * 3) + 5) + 5)") | |
| found! | |
| */ |
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https://eloquentjavascript.net/03_functions.html