/**

* @link https://leetcode.com/problems/trapping-rain-water/

* @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.

* (better see an image at the link)

* @param {Object []} heights

* @returns {Number}

*/

export default (heights) => {

const maxes = new Array(heights.length).fill(0);

let leftMax = 0;

for (let i = 0; i < heights.length; i += 1) {

const height = heights[i];

maxes[i] = leftMax;

leftMax = Math.max(leftMax, height);

}

let rightMax = 0;

for (let i = heights.length - 1; i >= 0; i -= 1) {

const height = heights[i];

const minHeight = Math.min(rightMax, maxes[i]);

if (height < minHeight) {

maxes[i] = minHeight - height;

} else {

maxes[i] = 0;

}

rightMax = Math.max(rightMax, height);

}

const result = maxes.reduce((acc, max) => (acc += max), 0);

return result;

};