说明：  给定N个非负整数a1，a2，。。。。a，其中每个表示坐标（i，ai）处的点。绘制N条垂直线，使得线i的两个端点位于（i，ai）和（i，0）。找到两条线，它们与x轴一起形成一个容器，使其包含最多的水。
(Given N non-negative integers a1,a2,....an where each represents a point at coordinate (i, ai). N vertical lines are drawn such that the two endpoints of line i is at (i, ai) and (i,0). Find two lines, which together with x-axis forms a container, such that it contains the most water.)