【LeetCode】Trapping Rain Water

class Solution {
public:
    int trap(int A[], int n) {
        vector<int> left(n);
	int maxheight = 0;
	for (int i = 0; i < n; i++)
	{
		left[i] = maxheight;
		maxheight = max(maxheight, A[i]);
	}
	vector<int> right(n);
	maxheight = 0;
	for (int i = n - 1; i >= 0; i--)
	{
		right[i] = maxheight;
		maxheight = max(maxheight, A[i]);
	}

	int result = 0;
	for (int i = 0; i < n; i++)
	{
		int height = min(left[i], right[i]) - A[i];
		if (height < 0)
			height = 0;
		result += height;
	}
	return result;
    }
};