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], return6.

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. Thanks Marcos for contributing this image!

public class Solution {
    public int trap(int[] A) {
        /*计算最高的位置，那么它两边的水就取决于左边高度和右边高度*/
        int maxIndex=0;
        for(int i=0;iA[maxIndex]){
                maxIndex=i;
            }
        }
        int left=0,right=0;
        int sum=0;
        for(int i=0;imaxIndex;i--){
            if(A[i]