Problem: https://mirror.codeforces.com/contest/1620/problem/E

I was trying to apply some dsu-like logic in Problem E, when they asked for replacement of every $$$x$$$ with $$$y$$$ in the array, but it gave me WA on test 4.

The idea which I used during the contest:

from = replacement[x], to = replacement[y]
while(replacement[to] != to) to = replacement[to];
replacement[from] = to;

And, the idea which gave AC after the contest,

replacement[x] = replacement[y]

I know that the latter one is clever and more sleek, but why the former one fails? Can anyone please suggest a counter-case for it?

Except for these idea, the rest of code was exact same!

Submission 1 (with first logic): https://mirror.codeforces.com/contest/1620/submission/139872871
Submission 2 (with second logic): https://mirror.codeforces.com/contest/1620/submission/139872969