#42 - Trapping Rain Water

Hard • View on LeetCode • View on GitHub

Problem Description

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.

Solution

/**
 * @param {number[]} height
 * @return {number}
 */
var trap = function(height) {
  let result = 0;

  for (let left = 0, right = height.length - 1, maxL = 0, maxR = 0; left < right;) {
    maxL = Math.max(maxL, height[left]);
    maxR = Math.max(maxR, height[right]);
    result += maxL < maxR ? maxL - height[left++] : maxR - height[right--];
  }

  return result;
};