Renewal LDBC Datagen

1. Distance Hop Generator

add DistanceHopKnowsGenerator.java to generate social networks faster

use alpha to control Clustering Coefficient

2. Diameter Generator (in the Diameter branch, cover the original version)

1. connect the network (DistanceHopKnowsGenerator.java, line 23)
2. add edges in each block (DistanceHopKnowsGenerator.java, line 45)
3. trace the head and the tail vertex in each group (HadoopKnowsGenrator.java, line 90)
4. add edges between the head and the tail vertices among groups (HadoopMergeFriendshipFiles.java, line 53)

NOTE: do not shuffle the persons