0875. Koko Eating Bananas.js

// Koko loves to eat bananas.  There are N piles of bananas, the i-th 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 won't eat any more bananas during this hour.
// Koko likes to eat slowly, but still wants to finish eating all the bananas before the guards come back.
// 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
//
// Note:
//
// 1 <= piles.length <= 10^4
// piles.length <= H <= 10^9
// 1 <= piles[i] <= 10^9

/**
 * @param {number[]} piles
 * @param {number} H
 * @return {number}
 */

// Time O(N log W), where N is the number of piles, and W is the maximum size of a pile
// Space O(1)
const minEatingSpeed = (piles, H) => {
  const canEatAll = (speed) => {
    let time = 0;
    for (const p of piles) {
      time += Math.ceil(p / speed);
    }
    return time <= H;
  };

  let l = 0;
  let r = Math.max(...piles); // when the max speed = biggest pile, it only needs 1h to eat each pile
  while (l < r) {
    const m = ~~((l + r) / 2);
    if (!canEatAll(m)) l = m + 1;
    else r = m;
  }
  return l;
};