Function that finds all the local maximas in a vector of unsigned integers

main.rs

/// Given an array of integers, return the index of each local peak in the array.
/// A “peak” element is an element that is greater than its neighbors.
///
/// Example:
///
/// ```
/// $ localPeaks([1,2,3,1])
/// $ [2]
///
/// $ localPeaks([1,3,2,3,5,6,4])
/// $ [1, 5]
/// ```
fn main() {
    let mut max = local_maximas(vec![1, 2, 3, 1]);
    println!("{:?}", max);

    max = local_maximas(vec![1, 3, 2, 3, 5, 6, 4]);
    println!("{:?}", max);
}

fn local_maximas(nums: Vec<usize>) -> Option<Vec<usize>> {
    match nums.len() {
        0 => return None,
        1 => return Some(vec![0]),
        _ => {}
    };

    let mut max: Vec<usize> = Vec::new();
    let mut prev = usize::MIN;
    let mut last: &[usize] = &vec![];

    for (i, n) in nums.windows(2).enumerate() {
        if prev < n[0] && n[0] > n[1] {
            max.push(i);
        }
        prev = n[0];
        last = n.clone();
    }

    // Handle the last element as a special due to how the `windows` API from
    // itertools work.
    if last[1] > last[0] {
        max.push(nums.len() - 1);
    }

    match max.len() {
        0 => None,
        _ => Some(max),
    }
}

#[cfg(test)]
mod tests {
    use super::local_maximas;

    #[test]
    fn it_works() {
        assert_eq!(local_maximas(vec![1, 2, 3, 1]), Some(vec![2]));
        assert_eq!(local_maximas(vec![1, 3, 2, 3, 5, 6, 4]), Some(vec![1, 5]));
        assert_eq!(local_maximas(vec![1, 2, 3, 4]), Some(vec![3]));
        assert_eq!(local_maximas(vec![4, 3, 2, 1]), Some(vec![0]));
        assert_eq!(local_maximas(vec![9]), Some(vec![0]));
        assert_eq!(local_maximas(vec![]), None);

        // special case where there is a plateau instead of a peak
        assert_eq!(local_maximas(vec![1, 2, 2, 2, 1]), None);
    }
}