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36 lines
1.1 KiB
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36 lines
1.1 KiB
Markdown
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---
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minutes: 30
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---
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# Exercise: Collatz Sequence
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The [Collatz Sequence](https://en.wikipedia.org/wiki/Collatz_conjecture) is
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defined as follows, for an arbitrary n<sub>1</sub> greater than zero:
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- If _n<sub>i</sub>_ is 1, then the sequence terminates at _n<sub>i</sub>_.
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- If _n<sub>i</sub>_ is even, then _n<sub>i+1</sub> = n<sub>i</sub> / 2_.
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- If _n<sub>i</sub>_ is odd, then _n<sub>i+1</sub> = 3 * n<sub>i</sub> + 1_.
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For example, beginning with _n<sub>1</sub>_ = 3:
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* 3 is odd, so _n<sub>2</sub>_ = 3 * 3 + 1 = 10;
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* 10 is even, so _n<sub>3</sub>_ = 10 / 2 = 5;
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* 5 is odd, so _n<sub>4</sub>_ = 3 * 15 + 1 = 16;
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* 16 is even, so _n<sub>5</sub>_ = 16 / 2 = 8;
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* 8 is even, so _n<sub>6</sub>_ = 8 / 2 = 4;
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* 4 is even, so _n<sub>7</sub>_ = 4 / 2 = 2;
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* 2 is even, so _n<sub>8</sub>_ = 1; and
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* the sequence terminates.
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Write a function to calculate the length of the collatz sequence for a given
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initial `n`.
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```rust,should_panic
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{{#include exercise.rs:collatz_length}}
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todo!("Implement this")
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}
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{{#include exercise.rs:main}}
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todo!("Implement this")
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}
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```
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