LeetCode-Max Points on a Line[AC源码]

  1 package com.lw.leet3;
  2 
  3 import java.util.HashMap;
  4 import java.util.Iterator;
  5 import java.util.Map;
  6 import java.util.Map.Entry;
  7 
  8 
  9 /**
 10  * @ClassName:Solution
 11  * @Description:Max Points on a Line 
 12  *         Given n points on a 2D plane, find the maximum number of points that 
 13  *         lie on the same straight line.
 14  * @Author LiuWei
 15  * @Date 2014年8月17日下午2:51:08
 16  * @Mail nashiyue1314@163.com 
 17  */
 18 
 19 /**
 20  * Definition for a point.
 21  * class Point {
 22  *     int x;
 23  *     int y;
 24  *     Point() { x = 0; y = 0; }
 25  *     Point(int a, int b) { x = a; y = b; }
 26  * }
 27  */
 28 
 29 public class Solution {
 30 
 31     public int maxPoints(Point[] points) {
 32         int max = 0;
 33         if(points.length <= 2){
 34             max = points.length;
 35         }
 36         else{
 37             for(int i = 0; i < points.length; i++){
 38                 int equalNum = 0;
 39                 Map<Double, Integer> map = new HashMap<Double, Integer>();
 40                 for(int j = i+1; j < points.length; j++ ){
 41                     if(points[i].x == points[j].x && points[i].y == points[j].y){
 42                         equalNum ++;
 43                         continue;
 44                     }
 45                     
 46                     double k = 0;
 47                     if(points[i].x == points[j].x){
 48                         k = Double.MAX_VALUE;
 49                     }
 50                     else{
 51                         k = ((double)(points[i].y - points[j].y)/(points[i].x - points[j].x));
 52                         /**
 53                          * Submission Result: Wrong Answer
 54                          * Input:    [(2,3),(3,3),(-5,3)]
 55                          * Output:    2
 56                          * Expected:3
 57                          * 
 58                          * avoid k = +0.0 -0.0
 59                          * */
 60                         if(k == 0){
 61                             k = 0; 
 62                         }
 63                     }
 64                     
 65                     if(map.containsKey(k)){
 66                         map.put(k, map.get(k)+1);
 67                     }
 68                     else{
 69                         map.put(k, 2);
 70                     }
 71                 }
 72                 
 73                 /**
 74                  * Submission Result: Wrong Answer
 75                  * Input:    [(1,1),(1,1),(1,1)]
 76                  * Output:    0
 77                  * Expected:3
 78                  * 
 79                  * avoid the points are all equal
 80                  * */
 81                 if(equalNum > max){
 82                     max = equalNum + 1 ;
 83                 }
 84                 Iterator<Entry<Double, Integer>> iter = map.entrySet().iterator();
 85                 while(iter.hasNext()){
 86                     Entry<Double, Integer> entry = iter.next();
 87                     int num = entry.getValue();
 88                     if( num + equalNum > max){
 89                         max = num + equalNum; 
 90                     }
 91                 }
 92             }
 93         }
 94         return max;
 95     }
 96     
 97     public static void main(String[] args){
 98         Point[] p = {new Point(2, 3),new Point(3,3),new Point(-5,3)};
 99 //        Point[] p = {new Point(1, 1),new Point(1,1),new Point(1,1)};
100         
101         Solution s = new Solution();
102         System.out.println(s.maxPoints(p));
103         
104     }
105     
106 }