mapreduce '找共同朋友'，面试题

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mapred找共同朋友，数据格式如下：

[quote]
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
[/quote]

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


答案如下：

import java.io.IOException;import java.util.Set;import java.util.StringTokenizer;import java.util.TreeSet;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.Reducer;import org.apache.hadoop.mapreduce.Mapper.Context;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import org.apache.hadoop.util.GenericOptionsParser;public class FindFriend {          public static class ChangeMapper extends Mapper<Object, Text, Text, Text>{                                         @Override                   public void map(Object key, Text value, Context context) throws IOException, InterruptedException {                             StringTokenizer itr = new StringTokenizer(value.toString());                                 Text owner = new Text();                                 Set<String> set = new TreeSet<String>();                             owner.set(itr.nextToken());                             while (itr.hasMoreTokens()) {                                     set.add(itr.nextToken());                             }                                          String[] friends = new String[set.size()];                             friends = set.toArray(friends);                             for(int i=0;i<friends.length;i++){                                     for(int j=i+1;j<friends.length;j++){                                             String outputkey = friends[i]+friends[j];                                             context.write(new Text(outputkey),owner);                                     }                                                                  }                   }          }          public static class FindReducer extends Reducer<Text,Text,Text,Text> {                                                  public void reduce(Text key, Iterable<Text> values,                                         Context context) throws IOException, InterruptedException {                                  String  commonfriends ="";                               for (Text val : values) {                                  if(commonfriends == ""){                                          commonfriends = val.toString();                                  }else{                                          commonfriends = commonfriends+":"+val.toString();                                  }                               }                              context.write(key, new Text(commonfriends));                                                        }                                    }        public static void main(String[] args) throws IOException,        InterruptedException, ClassNotFoundException {            Configuration conf = new Configuration();            String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();            if (otherArgs.length < 2) {              System.err.println("args error");              System.exit(2);            }            Job job = new Job(conf, "word count");            job.setJarByClass(FindFriend.class);            job.setMapperClass(ChangeMapper.class);            job.setCombinerClass(FindReducer.class);            job.setReducerClass(FindReducer.class);            job.setOutputKeyClass(Text.class);            job.setOutputValueClass(Text.class);            for (int i = 0; i < otherArgs.length - 1; ++i) {              FileInputFormat.addInputPath(job, new Path(otherArgs[i]));            }            FileOutputFormat.setOutputPath(job,              new Path(otherArgs[otherArgs.length - 1]));            System.exit(job.waitForCompletion(true) ? 0 : 1);        }}

运行结果：

AB      E:C:DAC      E:BAD      B:EAE      C:B:DBC      A:EBD      A:EBE      C:D:ABF      ACD      E:A:BCE      A:BCF      ADE      B:ADF      AEF      A

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