[Leetcode]42 trapping Rain water

https://oj.leetcode.com/problems/trapping-rain-water/

Http://fisherlei.blogspot.com/2013/01/leetcode-trapping-rain-water.html

Public class solution {    public int trap (Int[] A)  {                      //  for a coordinate   has         // - leftmax  It left highest         // - rightmax  it right up          // - val  it itself highly         //   then its volume is  max ( min (Leftmax, rightmax)  - val, 0 )                  //  traverse from left to right   create   leftmax[]        //  similar   right-to-left traversal   Create  rightmax[]         //  finally traverse through   calculate volume   sum          // o (n)                 // Input  validations.        if  (a == null | |  a.length == 0)             return  0;   // Invalid input.                 int len = A.length;                 // Build leftmax[]         int[] leftmax = new int[len];         int seenleftmax = 0;        for   (int i = 0 ; i < len ; i ++)          {            leftmax[i] = seenleftmax;             if  (A[i] > seenleftmax)                  seenleftmax =  A[i];        }                 // Build rightmax[]         int[] rightmax = new int[len];         int seenrightmax = 0;        for  (int i  = len - 1 ; i >= 0 ; i --)          {            rightmax[i]  = seenrightmax;            if  (A[i] >  Seenrightmax)                  seenrightmax = a[i];        }                 // Calculate result         int result = 0;         for  (int i = 0 ; i < len ; i ++)          {             Int v = math.max (Math.min (Leftmax[i], rightmax[i])  - a[i] , 0);             result += v;         }        return result;    }} 

[Leetcode]42 trapping Rain water