Please study the following problems related to
graphs:
1.
http://acm.uva.es/p/v5/515.html
2.
http://acm.uva.es/p/v5/563.html
3.
http://acm.uva.es/p/v105/10506.html
4.
http://acm.uva.es/p/v106/10615.html
5.
http://acm.uva.es/p/v106/10630.html
6.
http://acm.uva.es/p/v107/10735.html
7.
http://acmicpc-live-archive.uva.es/nuevoportal/data/problem.php?p=2099