The solution I tried to implement, but because I didn't know about cloned() method had to go with clonning input array into variable -__-

Do you know you can fork the solution and see what happens if you remove this part? Just click on fork below the code. Rust compiler explains things very well :)

Tell me you r a compiler dev without telling me you r a compiler dev

Clever.

I have a similar algorithm. The entry(idx).or_insert(i) is unnecessary, you may do insert(idx, i). and the char in stack is not needed as well.

Nice! I wish slice::array_windows was stable, that would let you do something like:

.filter(|[a, b, c]| {
  a != b && b == c
})