356. Line Reflection

Given n points on a 2D plane, find if there is such a line parallel to y-axis that reflect the given points.

Example 1:

Given points = [[1,1],[-1,1]], return true.

Example 2:

Given points = [[1,1],[-1,-1]], return false.

Follow up:
Could you do better than O(n2)?

 

本题目要求求一个平行于y轴的直线，看points是否对于y轴对称。实现起来比较简单，对称的线肯定是最大和最小点正中间的线，推理如下代码如下：

 1 public class Solution {
 2     public boolean isReflected(int[][] points) {
 3         int min = Integer.MAX_VALUE;
 4         int max = Integer.MIN_VALUE;
 5         Set<String> set = new HashSet<String>();
 6         for(int[] p:points){
 7             min = Math.min(p[0],min);
 8             max = Math.max(p[0],max);
 9             String str = p[0]+"a"+p[1];
10             set.add(str);
11         }
12         int sum = min+max;
13         for(int[] p:points){
14             String str = (sum-p[0]+"a"+p[1]);
15             if(!set.contains(str)) return false;
16         }
17         return true;
18     }
19 }