### LeetCode Challenge #42. Trapping Rain Water

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
```

Constraints:

• `n == height.length`
• `1 <= n <= 2 * 104`
• `0 <= height[i] <= 105`
##### Video Solution
###### Java Solution
```				```
class Solution {
public int trap(int[] height) {
int n = height.length ;
int[] leftMax = new int[n];
leftMax=height;

for(int i=1;i<n;i++){
leftMax[i] = Math.max(leftMax[i-1],height[i]);
}

int[] rightMax = new int[n];
rightMax[n-1]=height[n-1];
for(int i=n-2;i>=0;i--){
rightMax[i] = Math.max(rightMax[i+1],height[i]);
}

int ans = 0 ;
for(int i=0;i<n;i++){
ans += Math.min(leftMax[i],rightMax[i])-height[i];
}

return ans ;
}
}
```
```