0875-koko-eating-bananas.rs

use std::cmp::Ordering::{Equal, Less, Greater};

impl Solution {
    pub fn min_eating_speed(piles: Vec<i32>, h: i32) -> i32 {
        let max_piles = *piles.iter().max().unwrap() as usize;
        let (mut l, mut r) = (1, max_piles);
        let mut k = max_piles;

        while l <= r {
            let m = l + (r - l) / 2;
            let hrs: usize = piles.iter()
                .map(|&num_bananas| ((num_bananas - 1) as usize / m) + 1)
                .sum();

            match hrs.cmp(&(h as usize)) {
                Less | Equal => {
                    k = k.min(m);
                    r = m - 1;
                },
                Greater => l = m + 1, 
            }
        }

        k as i32
    }
}