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104 lines
2.8 KiB
Markdown
104 lines
2.8 KiB
Markdown
---
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id: 6821ebf8237de8297eaee798
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title: "Challenge 22: Tribonacci Sequence"
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challengeType: 29
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dashedName: challenge-22
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---
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# --description--
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The Tribonacci sequence is a series of numbers where each number is the sum of the three preceding ones. When starting with `0`, `0` and `1`, the first 10 numbers in the sequence are `0`, `0`, `1`, `1`, `2`, `4`, `7`, `13`, `24`, `44`.
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Given an array containing the first three numbers of a Tribonacci sequence, and an integer representing the length of the sequence, return an array containing the sequence of the given length.
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- Your function should handle sequences of any length greater than or equal to zero.
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- If the length is zero, return an empty array.
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- Note that the starting numbers are part of the sequence.
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# --hints--
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`tribonacci_sequence([0, 0, 1], 20)` should return `[0, 0, 1, 1, 2, 4, 7, 13, 24, 44, 81, 149, 274, 504, 927, 1705, 3136, 5768, 10609, 19513]`.
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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(tribonacci_sequence([0, 0, 1], 20), [0, 0, 1, 1, 2, 4, 7, 13, 24, 44, 81, 149, 274, 504, 927, 1705, 3136, 5768, 10609, 19513])`)
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}})
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```
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`tribonacci_sequence([21, 32, 43], 1)` should return `[21]`.
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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(tribonacci_sequence([21, 32, 43], 1), [21])`)
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}})
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```
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`tribonacci_sequence([0, 0, 1], 0)` should return `[]`.
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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(tribonacci_sequence([0, 0, 1], 0), [])`)
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}})
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```
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`tribonacci_sequence([10, 20, 30], 2)` should return `[10, 20]`.
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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(tribonacci_sequence([10, 20, 30], 2), [10, 20])`)
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}})
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```
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`tribonacci_sequence([10, 20, 30], 3)` should return `[10, 20, 30]`.
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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(tribonacci_sequence([10, 20, 30], 3), [10, 20, 30])`)
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}})
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```
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`tribonacci_sequence([123, 456, 789], 8)` should return `[123, 456, 789, 1368, 2613, 4770, 8751, 16134]`.
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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(tribonacci_sequence([123, 456, 789], 8), [123, 456, 789, 1368, 2613, 4770, 8751, 16134])`)
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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 tribonacci_sequence(start_sequence, length):
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return length
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```
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# --solutions--
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```py
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def tribonacci_sequence(start_sequence, length):
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if length == 0:
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return []
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if length == 1:
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return [start_sequence[0]]
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if length == 2:
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return [start_sequence[0], start_sequence[1]]
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if length == 3:
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return start_sequence[:]
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sequence = start_sequence[:]
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while len(sequence) < length:
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next_value = sequence[-1] + sequence[-2] + sequence[-3]
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sequence.append(next_value)
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return sequence
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```
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