Maximum width ramp in Rust (https://leetcode.com/problems/maximum-width-ramp/)

maximum_width_ramp.rs

impl Solution {
    pub fn max_width_ramp(a: Vec<i32>) -> i32 {
        let mut largest: Vec<usize> = vec![(a.len()-1) as usize];
        for (i, val) in a.iter().enumerate().rev().skip(1) {
            if *val > a[*largest.last().unwrap()] {
                largest.push(i);
            }
        }
        let mut max_width = 0;
        for (i, val) in a.iter().enumerate() {
            while !largest.is_empty() && *val <= a[*largest.last().unwrap()] {
                max_width = std::cmp::max(max_width, largest.pop().unwrap() - i);
            }
        }
        max_width as i32
    }
}