After a small discussion, we decided to publish the generator that causes #TLE of HashSet and HashMap in Java.

It is here — http://pastebin.com/qpyNcD3R

The main idea: let's force the hash collections to put all the items in one bucket.

A feature of HashSet and HashMap is a usage of a special linear hash transformation, and then use a reminder hash % bucketsCount as bucket number.

This is some quotes from original Java code:

```
static int hash(int h) {
// This function ensures that hashCodes that differ only by
// constant multiples at each bit position have a bounded
// number of collisions (approximately 8 at default load factor).
h ^= (h >>> 20) ^ (h >>> 12);
return h ^ (h >>> 7) ^ (h >>> 4);
}
static int indexFor(int h, int length) {
return h & (length-1); /*length is a power of 2 --- me*/
}
```

The only difficulty is to generate an inverse transform — it is here:

```
int hashinv(int h) {
h ^= (h >>> 4) ^ (h >>> 7) ^ (h >>> 8) ^ (h >>> 14) ^ (h >>> 15)
^ (h >>> 18) ^ (h >>> 19) ^ (h >>> 20) ^ (h >>> 21)
^ (h >>> 23) ^ (h >>> 26) ^ (h >>> 28);
return h;
}
```

And then, just type the numbers in a such way:

```
final int size = 100000;
int[] s = new int[size];
for (int i = 0, val = 0; i < size; i++) {
s[i] = Integer.MAX_VALUE;
while (s[i] > 1000000000)
s[i] = hashinv(bitreverse(val++));
}
```

Here, bitreverse inverses last 31 bits in number.

This works for Java 6 и Java 7 with almost all standard input transformation (sorting, random shuffling, etc).

Good luck in hacks!

Well, then the question arises.. what should I use then?!

Hmm... TreeMap and compareTo instead of HashMap and hashCode?

It seems to take a lot of time to find enough numbers less than 100000 while it barely take time to find enough numbers less than 1000000000.

Do you want to find 100000 different positive integer numbers less than 100000?

I got it!

T.T

What about if I change the load factor?

As I know bucketsCount would be different and the code for hacking should be different (I guess).

No, if

`a == b`

, then`(a == b) mod M`

for every M. Look, first the hash is calculated as shown above and the operation % is used by module bucketsCount. The first phase doesn't work.