Please study
the following problems related to grids.
1.
http://acm.uva.es/p/v101/10161.html
2.
http://acm.uva.es/p/v100/10047.html
3.
http://acm.uva.es/p/v101/10159.html
4.
http://acm.uva.es/p/v101/10182.html
5.
http://acm.uva.es/p/v7/707.html
6.
http://acm.uva.es/p/v101/10177.html