Trapping Rain Water

 1 package StacksAndqueues;
 2 
 3 public class TrappingRainWater {
 4 
 5     public static void main(String[] args) {
 6         // TODO Auto-generated method stub
 7         //从左往右找到最大，再从右到左找到最大，目前最大-目前array[i];找到其中最小的，即为存水量。
 8     int[] array= {0,1,0,2,1,0,1,3,2,1,2,1};
 9     System.out.println(trap(array));
10     }
11 
12     public static int trap(int[] array) {
13         if (array.length == 0)
14             return 0;
15         int len = array.length - 1;
16         int[] maxl = new int[len + 1];
17         int[] maxr = new int[len + 1];
18         int cap = 0, total = 0;
19         for (int i = len; i >= 0; i--) {
20             maxr[i] = cap;
21             if (array[i] > cap)
22                 cap = array[i];
23         }
24         cap = 0;
25         for (int i = 0; i <= len; i++) {
26             maxl[i] = cap;
27             if (array[i] > cap)
28                 cap = array[i];
29         }
30         for (int i = 0; i <= len; i++) {
31             int c = Math.min(maxl[i], maxr[i]) - array[i];
32             if (c > 0)
33                 total += c;
34         }
35         return total;
36     }
37 }