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85 lines
1.5 KiB
Markdown
85 lines
1.5 KiB
Markdown
---
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id: 69306364df283fcaff2e1ad6
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title: "Challenge 145: Nth Fibonacci Number"
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challengeType: 29
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dashedName: challenge-145
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---
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# --description--
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Given an integer `n`, return the `n`th number in the fibonacci sequence.
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The Fibonacci sequence is a series of numbers where each number is the sum of the two preceding ones. The first 10 numbers in the sequence are `0`, `1`, `1`, `2`, `3`, `5`, `8`, `13`, `21`, `34`.
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# --hints--
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`nth_fibonacci(4)` should return `2`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(nth_fibonacci(4), 2)`)
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}})
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```
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`nth_fibonacci(10)` should return `34`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(nth_fibonacci(10), 34)`)
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}})
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```
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`nth_fibonacci(15)` should return `377`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(nth_fibonacci(15), 377)`)
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}})
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```
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`nth_fibonacci(40)` should return `63245986`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(nth_fibonacci(40), 63245986)`)
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}})
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```
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`nth_fibonacci(75)` should return `1304969544928657`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(nth_fibonacci(75), 1304969544928657)`)
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}})
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```
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# --seed--
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## --seed-contents--
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```py
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def nth_fibonacci(n):
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return n
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```
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# --solutions--
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```py
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def nth_fibonacci(n):
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if n == 1:
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return 0
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if n == 2:
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return 1
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a, b = 0, 1
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for _ in range(3, n + 1):
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a, b = b, a + b
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return b
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```
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