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)?

Analysis: If there is a line parallel to Y-axis, then the left-most and the right-most must be reflected by that line. 

public class Solution {
    public boolean isReflected(int[][] points) {
        if (points == null) return true;
        int n = points.length;
        if (n < 2) return true;
        
        HashSet<String> set = new HashSet<String>();
        int maxValue = Integer.MIN_VALUE, minValue = Integer.MAX_VALUE;
        for (int i = 0; i < n; i++) {
            maxValue = Math.max(maxValue, points[i][0]);
            minValue = Math.min(minValue, points[i][0]);
            set.add(points[i][0] + "," + points[i][1]);
        }
        
        int sum = maxValue + minValue;
        for (int i = 0; i < n; i++) {
            String findMe = (sum - points[i][0]) + "," + points[i][1];
            if (!set.contains(findMe)) return false;
        }
        return true;
    }
}