Create HopcroftKarp.java

Sample Input-Ouput:

Input 1:
4
1 1001
2 1002
5 1004
4 1005

Output 1:
4

Input 2:
4
1 1001
2 1001
3 1002
3 1002

Output 2:
2

Assumption: The max number of nodes in all is 2000.
Number of nodes in one set of bipartite graph: 1 - 1000
Number of nodes in another set of bipartite graph: 1001 - 2000