Leetcode: 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 is able to trap after raining.

For example, 
Given [0,1,0,2,1,0,1,3,2,1,2,1], return 6.

The above elevation map 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.

Solution:

public class Solution {
    public int trap(int[] A) {
        int max = 0;
        int maxIndex=0;
        for(int i=0; i< A.length; i++)
        {
            if(A[i]>max)
            {  
                max = A[i];
                maxIndex = i;
            }
        }
        
        int prevMax = 0;
        int count = 0;
        for(int i=0; i<maxIndex; i++)
        {
            if(A[i]>prevMax)
                prevMax = A[i];
            count += prevMax - A[i];
        }
        
        prevMax = 0;
        for(int i=A.length-1; i>maxIndex; i--)
        {
            if(A[i]>prevMax)
                prevMax = A[i];
            count += prevMax -A[i];
        }
        return count;
    }
}