Max Points on a line

Change-Id: I46f37795eec9462c942f4b5e87c74b800b6ce195

Author: applewjg

MaxPointsOnALine.java

@@ -0,0 +1,46 @@
+/*
+ Author:     Andy, [email protected]
+ Date:       Dec 03, 2014
+ Problem:    Max Points On a Line
+ Difficulty: Easy
+ Notes:
+ Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.
+ Solution: 1. hashmap. Time: O(n^2), Space: O(n);
+*/
+
+/**
+ * Definition for a point.
+ * class Point {
+ *     int x;
+ *     int y;
+ *     Point() { x = 0; y = 0; }
+ *     Point(int a, int b) { x = a; y = b; }
+ * }
+ */
+public class Solution {
+    public int maxPoints(Point[] points) {
+        int res = 0;
+        int N = points.length;
+        for (int i = 0; i < N; ++i) {
+            HashMap<Double, Integer> m = new HashMap<Double, Integer>();
+            int ss = 1, sp = 0;
+            for (int j = i + 1; j < N; ++j) {
+                double slope = Double.MIN_VALUE;
+                if (points[i].x != points[j].x) {
+                    slope = (double)(points[i].y - points[j].y) / (points[i].x - points[j].x);
+                    if (slope == -0.0) slope = 0.0;
+                } else if (points[i].y == points[j].y) {
+                    sp += 1; continue;
+                }
+                int tmp = 2;
+                if (m.containsKey(slope)) {
+                    tmp = m.get(slope) + 1;
+                }
+                m.put(slope, tmp);
+                ss = Math.max(ss, tmp);
+            }
+            res = Math.max(res, ss + sp);
+        }
+        return res; 
+    }
+}