I am very new on Leetcode. I was doing the Slowest Key problem in September Leetcoding challenge 2021. The Best submission had this snippet of code at the top :

static const auto speedup = {
ios_base::sync_with_stdio(false);
cout.tie(NULL);
cin.tie(NULL);
return NULL;
}();

Can someone explain how this code works?
I used it in my submission and my 4 ms runtime became 0ms. How is this possible?