Week 12 - Combinatorics

Question

The tasks for week 12 are as follows:

Week problem: 11401 Triangle Counting
Weekend problem: 00991 Safe Salutations
Suggested bonus: 11310 Delivery Debacle

You must submit your solutions on http://uva.onlinejudge.org/

You can browse to these problems from the online judge website by clicking on Browse Problems, Contest Volumes, and then selecting the contest volume as indicated above.

Comments

Please post below which of the questions you have been able to finish.

For each task, please let us know how much time you have spent on understanding / coding / debugging.

For each task let us know what the hardest part was. (This can be anything, ranging from not having read the problem to forgetting about a border case, to a semicolon in the wrong spot that screwed up an if-statement...)