In my hundreds of submissions, this is my first time encountering this Singular Iterator Runtime Error. In my submission 86437246, after passing the first few cases and when it encounters a relatively bigger input, the program exits with a RE. After looking at the diagnostic hints, I think it has something to do with singular iterators ( which is sort of equivalent to uninitialized pointers ), though I couldn't pinpoint where. But if I were to make a guess, I would say vector< pair< int, int > > which[1050] should be the source of the problem as after using some alternatives for it, I managed to get my solution accepted (86437933).

It would be very helpful if someone can throw some light on where I went wrong, so that I could avoid this in my future submissions.

**UPD:- ** It is a normal out of bounds error. Increasing the size of vis array takes care of it. Corrected submission — 86473660. Thanks WAontest2

Thanks a lot!

Edit:- I misunderstood the problem statement, my bad. There is no problem with the Jury.

So, while solving random problems from the problemset I came across the problem 1114D - Flood Fill. After wracking my brain for so long I couldn't come up with any solution within the given constraints.

But when I looked at all the submissions, almost everyone approached it in the same incorrect way. It is wrong, as I have a counter test cases for these solutions, which are almost the same as the editorial.

For example, let's take the editorial submission — 49738289 . For the test case

5
1 2 1 3 1

Actual Answer

It's obvious the answer is 2. Change the 2nd and 4th cell into 1, and bingo you have the same color everywhere in 2 moves.

Program's Output

If you run it locally and check, you will find it outputting 3. This, I believe , is also the Jury's Solution,

Actual Solution

I believe the actual solution is a DP which runs in cubic time, somewhat similar to the problem 1132F - Clear the String. But given the constraints, unless the test cases are weak, I highly doubt a cubic solution can pass. So the constraints as well as the Jury's solution needs to be changed.