solutions/2105-watering-plants-ii.js

/**
 * 2105. Watering Plants II
 * https://leetcode.com/problems/watering-plants-ii/
 * Difficulty: Medium
 *
 * Alice and Bob want to water n plants in their garden. The plants are arranged in a row and are
 * labeled from 0 to n - 1 from left to right where the ith plant is located at x = i.
 *
 * Each plant needs a specific amount of water. Alice and Bob have a watering can each, initially
 * full. They water the plants in the following way:
 * - Alice waters the plants in order from left to right, starting from the 0th plant. Bob waters
 *   the plants in order from right to left, starting from the (n - 1)th plant. They begin watering
 *   the plants simultaneously.
 * - It takes the same amount of time to water each plant regardless of how much water it needs.
 * - Alice/Bob must water the plant if they have enough in their can to fully water it. Otherwise,
 *   they first refill their can (instantaneously) then water the plant.
 * - In case both Alice and Bob reach the same plant, the one with more water currently in his/her
 *   watering can should water this plant. If they have the same amount of water, then Alice should
 *   water this plant.
 *
 * Given a 0-indexed integer array plants of n integers, where plants[i] is the amount of water the
 * ith plant needs, and two integers capacityA and capacityB representing the capacities of Alice's
 * and Bob's watering cans respectively, return the number of times they have to refill to water all
 * the plants.
 */

/**
 * @param {number[]} plants
 * @param {number} capacityA
 * @param {number} capacityB
 * @return {number}
 */
var minimumRefill = function(plants, capacityA, capacityB) {
  let result = 0;
  let left = 0;
  let right = plants.length - 1;
  let waterA = capacityA;
  let waterB = capacityB;

  while (left <= right) {
    if (left === right) {
      if (waterA >= waterB && waterA < plants[left]) result++;
      if (waterB > waterA && waterB < plants[right]) result++;
      break;
    }

    if (waterA < plants[left]) {
      waterA = capacityA;
      result++;
    }
    waterA -= plants[left++];

    if (waterB < plants[right]) {
      waterB = capacityB;
      result++;
    }
    waterB -= plants[right--];
  }

  return result;
};