Directional graph with a minimum number of circuits

Question

I have a problem, but I can not understand the solution. This happens as follows:

I have a directed graph with N nodes and M-links and without loops. I need to know the minimum number of chains, so each node belongs to only one chain.

Example:

7 11 7 knots; 11 links
1 2
1 5
2 3
2 5
2 7
3 4 // a link exists between 3 and 4
3 6
4 6
5 4
5 6
7 3

Answer: 2

Example: Chain: 2-7-3-6
Chain: 1-5-4

Thank.

Answer 1

, , - , . , -? .

: http://www2.cs.science.cmu.ac.th/person/rogaway/ps3-solns.pdf

, Hopcroft Karp: http://en.wikipedia.org/wiki/Hopcroft%E2%80%93Karp_algorithm