/*

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.

Example:1

Input: height = [0,1,0,2,1,0,1,3,2,1,2,1]

Output: 6

Explanation: The above elevation map (black section) is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped.

Example:2

Input: height = [4,2,0,3,2,5]

Output: 9

*/

using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(Trap(new int []{0,1,0,2,1,0,1,3,2,1,2,1}));

        Console.WriteLine(Trap(new int []{4,2,0,3,2,5}));

    }

    public static int Trap(int[] height) 

    {

        int total =0;

        int left = 0, right = height.Length-1;

        int lMax = 0, rMax=0;

        while(left <right)

        {

            if(height[left] < height[right])

            {

                if(height[left] > lMax)

                {

                    lMax = height[left];

                }

                else

                {

                    total += lMax - height[left];

                }

                left++;

            }

            else

            {

                if(height[right] > rMax)

                {

                    rMax = height[right];

                }

                else

                {

                    total += rMax - height[right];

                }

                right--;

            }

        }

        return total;

    }

}