Koko eating bananas

/*
 * Koko loves to eat bananas. There are n piles of bananas, the ith pile has piles[i] bananas. The guards have gone and will come back in h hours.
 * Koko can decide her bananas-per-hour eating speed of k. Each hour, she chooses some pile of bananas and eats k bananas from that pile. If the pile has less than k bananas, she eats all of them instead and will not eat any more bananas during this hour.
 * Koko likes to eat slowly but still wants to finish eating all the bananas before the guards return.
 * Return the minimum integer k such that she can eat all the bananas within h hours.
 * Example 1:
 * Input: piles = [3,6,7,11], h = 8
 * Output: 4
 * Example 2:
 * Input: piles = [30,11,23,4,20], h = 5
 * Output: 30
 * Example 3:
 * Input: piles = [30,11,23,4,20], h = 6
 * Output: 23
 * Constraints:
 * 1 <= piles.length <= 104
 * piles.length <= h <= 109
 * 1 <= piles[i] <= 109
 */

impl Solution {
  pub fn min_eating_speed(piles: Vec<i32>, h: i32) -> i32 {
    let mut lo = 1i32;
    let mut hi = *piles.iter().max().unwrap();
    while lo < hi {
      let mid = lo + (hi - lo) / 2;
      let hours: i64 = piles.iter().map(|&p| ((p as i64 + mid as i64 - 1) / mid as i64)).sum();
      if hours <= h as i64 { hi = mid; } else { lo = mid + 1; }
    }
    lo
  }
}