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

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img src="https://assets.leetcode.com/uploads/2018/10/22/rainwatertrap.png" style="width: 412px; height: 161px;" />
<pre>
<strong>Input:</strong> height = [0,1,0,2,1,0,1,3,2,1,2,1]
<strong>Output:</strong> 6
<strong>Explanation:</strong> 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.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> height = [4,2,0,3,2,5]
<strong>Output:</strong> 9
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>n == height.length</code></li>
	<li><code>1 &lt;= n &lt;= 2 * 10<sup>4</sup></code></li>
	<li><code>0 &lt;= height[i] &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:
    int trap(vector<int>& height) {
        if (height.size()<2)
        {
            return 0;
        }
        int startIndex = 0;
        while (height[startIndex]==0)
        {
            startIndex++;
        }
        int max = height[startIndex];
        int maxIndex = startIndex;

        int sumWaterDrop=0;
        int sumTemp=0;



        for (int i = startIndex; i < height.size(); i++)
        {

            if (max <= height[i])
            {
                max = height[i];
                maxIndex= i;
                sumWaterDrop += sumTemp;
                sumTemp = 0;
                continue;
            }
            sumTemp+=(max-height[i]);
        }
        startIndex = height.size()-1;
        while (height[startIndex]==0)
        {
            startIndex--;
        }
        sumTemp=0;
        int max2 = height[startIndex];
        int maxIndex2 = startIndex;


        for (int i = startIndex;i>=maxIndex;i--)
        {
            if (max2 <= height[i])
            {
                max2 = height[i];
                sumWaterDrop += sumTemp;

                sumTemp = 0;
                continue;
            }
            sumTemp+=(max2-height[i]);
        }
        return sumWaterDrop;
    }
};
 
24600