comprehensive-rust/src/control-flow-basics/exercise.rs

// Copyright 2023 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// ANCHOR: solution
// ANCHOR: collatz_length
/// Determine the length of the collatz sequence beginning at `n`.
fn collatz_length(mut n: i32) -> u32 {
    // ANCHOR_END: collatz_length
    let mut len = 1;
    while n > 1 {
        n = if n % 2 == 0 { n / 2 } else { 3 * n + 1 };
        len += 1;
    }
    len
}

// ANCHOR: tests
#[test]
fn test_collatz_length() {
    assert_eq!(collatz_length(11), 15);
}
// ANCHOR_END: tests

// ANCHOR: main
fn main() {
    // ANCHOR_END: main
    println!("Length: {}", collatz_length(11));
}