I notice that codeforces has no tag called random.
Usually,we don't use random in the contest because of the hack tests,but in practice,random can passed some problems (they have no test to hack random).
In some problems which have partial score, random can get high score and sometimes can get accepted.If someone use random in this situation,he may get high rank with easy code.
Some problems' solution is random,like random hash(maybe codeforces don't have these problems ?)
Many problems in contests can use random but we don't try like 197655937.We always think a right algorithm and it may cost many times.
I think random is a strange algorithm, how to use it?
(My English is pool :(
There are some problems with intended random solutions. They are rare, but very enjoyable. And codeforces should add such a tag.
In fact, if some problems use a trick with random, it is often tagged with "probabilities".
Sometimes the std of the problem itself is using random algorithm. If the accuracy of the algorithm is high enough to pass all the tests, then you don't have to worry about its correctness.
Nope. Try 1061F (interactive + random algorithm)