LeetCode 11. Container With Most Water

原题链接在这里：https://leetcode.com/problems/container-with-most-water/

题目：

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

题解：

双指针夹比，更新最大面积，每次移动小的那个夹板，因为储水量是由短的夹板决定的，移动大的夹板不会使面积更大.

Time Complexity: O(n). Space: O(1).

AC Java:

public class Solution {
    public int maxArea(int[] height) {
        if(height == null || height.length == 0){
            return 0;
        }
        int res = 0;
        int l = 0;
        int r = height.length-1;
        while(l<r){
            //r-l是底长, 取左右两侧高度较小者为高
            res = Math.max(res, (r-l) * Math.min(height[l], height[r]));
            //移动短的边
            if(height[l] < height[r]){
                l++;
            }else{
                r--;
            }
        }
        return res;
    }
}

类似Trapping Rain Water.