有趣的面试题

 

MR找共同朋友，数据格式如下：

 

A B C D E F
B A C D E
C A B E
D A B E
E A B C D
F A

 

第一字母表示本人，其他是他的朋友，找出有共同朋友的人，和共同朋友是谁

 

 1 import java.io.IOException;
 2 import java.util.Set;
 3 import java.util.StringTokenizer;
 4 import java.util.TreeSet;
 5 
 6 import org.apache.hadoop.conf.Configuration;
 7 import org.apache.hadoop.fs.Path;
 8 import org.apache.hadoop.io.Text;
 9 import org.apache.hadoop.mapreduce.Job;
10 import org.apache.hadoop.mapreduce.Mapper;
11 import org.apache.hadoop.mapreduce.Reducer;
12 import org.apache.hadoop.mapreduce.Mapper.Context;
13 import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
14 import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
15 import org.apache.hadoop.util.GenericOptionsParser;
16 
17 public class FindFriend {
18         
19           public static class ChangeMapper extends Mapper<Object, Text, Text, Text>{                      
20                    @Override
21                    public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
22                              StringTokenizer itr = new StringTokenizer(value.toString());
23                                  Text owner = new Text();
24                                  Set<String> set = new TreeSet<String>();
25                              owner.set(itr.nextToken());
26                              while (itr.hasMoreTokens()) {
27                                      set.add(itr.nextToken());
28                              }             
29                              String[] friends = new String[set.size()];
30                              friends = set.toArray(friends);
31                              
32                              for(int i=0;i<friends.length;i++){
33                                      for(int j=i+1;j<friends.length;j++){
34                                              String outputkey = friends[i]+friends[j];
35                                              context.write(new Text(outputkey),owner);
36                                      }                                     
37                              }
38                    }
39           }
40           
41           public static class FindReducer extends Reducer<Text,Text,Text,Text> {                          
42                         public void reduce(Text key, Iterable<Text> values, 
43                                         Context context) throws IOException, InterruptedException {
44                                   String  commonfriends =""; 
45                               for (Text val : values) {
46                                   if(commonfriends == ""){
47                                           commonfriends = val.toString();
48                                   }else{
49                                           commonfriends = commonfriends+":"+val.toString();
50                                   }
51                                }
52                               context.write(key, new Text(commonfriends));                                
53                         }                          
54           }
55           
56 
57         public static void main(String[] args) throws IOException,
58         InterruptedException, ClassNotFoundException {
59                 
60             Configuration conf = new Configuration();
61             String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
62             if (otherArgs.length < 2) {
63               System.err.println("args error");
64               System.exit(2);
65             }
66             Job job = new Job(conf, "word count");
67             job.setJarByClass(FindFriend.class);
68             job.setMapperClass(ChangeMapper.class);
69             job.setCombinerClass(FindReducer.class);
70             job.setReducerClass(FindReducer.class);
71             job.setOutputKeyClass(Text.class);
72             job.setOutputValueClass(Text.class);
73             for (int i = 0; i < otherArgs.length - 1; ++i) {
74               FileInputFormat.addInputPath(job, new Path(otherArgs[i]));
75             }
76             FileOutputFormat.setOutputPath(job,
77               new Path(otherArgs[otherArgs.length - 1]));
78             System.exit(job.waitForCompletion(true) ? 0 : 1);
79                 
80         }
81 
82 }

运行结果：

 

AB      E:C:D
AC      E:B
AD      B:E
AE      C:B:D
BC      A:E
BD      A:E
BE      C:D:A
BF      A
CD      E:A:B
CE      A:B
CF      A
DE      B:A
DF      A
EF      A

 

转自：http://www.aboutyun.com/thread-11107-1-1.html

 

posted @ 2015-03-16 14:46  Daem0n  阅读(676)  评论(0)  编辑  收藏  举报