42. 接雨水

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

 双指针解法。

public class Solution
{
    public int Trap(int[] height)
    {
        int size = height.Length, left = 0, right = size - 1, ans = 0, leftMax = 0, rightMax = 0;
        while (left < right)
        {
            if (height[left] < height[right])
            {
                if (height[left] >= leftMax)
                {
                    leftMax = height[left];
                }
                else
                {
                    ans += (leftMax - height[left]);
                }
                left++;
            }
            else
            {
                if (height[right] >= rightMax)
                {
                    rightMax = height[right];
                }
                else
                {
                    ans += (rightMax - height[right]);
                }
                right--;
            }
        }
        return ans;
    }
}