LeetCode Online Judge 题目C# 练习 - 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.

 1         public static int TrappingRainWater(int[] A)

 2         {

 3             if (A.Length <= 2)

 4                 return 0;

 5 

 6             int h = 0;

 7             // find the highest index

 8             for (int i = 0; i < A.Length; i++)

 9             {

10                 if (A[i] > A[h])

11                     h = i;

12             }

13 

14             int water = 0;

15             int p = 0;

16             // calculate from left to highest

17             for (int i = 1; i < h; i++)

18             {

19                 if (A[p] > A[i])

20                     water += A[p] - A[i];

21                 else

22                     p = i;

23             }

24 

25             p = A.Length - 1;

26             // calculate from right to highest

27             for (int i = A.Length - 2; i > h; i--)

28             {

29                 if (A[p] > A[i])

30                     water += A[p] - A[i];

31                 else

32                     p = i;

33             }

34 

35             return water;

36         }

代码分析：

　　这是我一开始复习就在别人的面经上看到的题，数数手指也快2年了，唉。。。。什么时候才能给我OFFER啊？？

　　1. 找到最高的index

　　2. 从左往右算water 的体积（面积）。p = 0， 如果A[i] < A[p]，差值就可以承载水，如果A[i] >= A[p] ，p = i

　　3. 从右往左在加一次water。 同理。