LeetCode42. 接雨水

class Solution {
    public int trap(int[] height) {
        if(height == null || height.length == 0) 
            return 0;
        int sumArea = 0;
        Stack<Integer> stack = new Stack<Integer>();
        for(int right = 0;right < height.length;right++) {
            while(!stack.isEmpty() && height[stack.peek()] < height[right]) { 
                if(stack.size() >= 2) {
                    int j = stack.pop();
                    int left = stack.peek();
                    int curArea = (Math.min(height[right],height[left]) - height[j]) * (right - left - 1);
                    sumArea += curArea;
                }
                else
                    stack.pop();
            }
            stack.push(right);
        }
        return sumArea;
    }
}