11. Container With Most Water

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 the container contains the most water.

Note: You may not slant the container and n is at least 2.

The above vertical lines are represented by array [1,8,6,2,5,4,8,3,7]. In this case, the max area of water (blue section) the container can contain is 49.

Example:

Input: [1,8,6,2,5,4,8,3,7]
Output: 49

容器的高度受限于短的竖线的长度，用首尾两个指针，差值为容器底长，每次较短的指针向中间靠拢，用ans储存面积最大值。

        public int maxArea(int[] height){
            int head = 0;
            int tail = height.length - 1;
            int ans = Math.min(height[head], height[tail]) * (tail - head);
            while (head < tail){
                //头指针短，则向有靠拢，反之亦然
                if (height[head] < height[tail] && head < tail)
                    head++;
                ans = Math.max(ans,Math.min(height[head], height[tail]) * (tail - head));
                if (height[tail] < height[head] && head < tail)
                    tail--;
                ans = Math.max(ans,Math.min(height[head], height[tail]) * (tail - head));
                if (height[head] == height[tail])
                    head ++;
            }
            return  ans;
        }