#pragma GCC optimize("O3", "unroll-loops")

auto init = []()
{ 
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    return 'c';
}();

https://leetcode.com/problems/leaf-similar-trees/solutions/4532722/c-dfs-recursion-vs-iteration-0ms-beats100/
https://codeforces.com/blog/entry/10