I was practising earlier today on this problem from the most recent contest. When I use a bitset of size 5005, I get a memory usage of 3688KB. When I use a bitset of size 50005, I get a memory usage of 31168KB. When I use a bitset of size 400005, I get a memory usage of a huge 244924KB! But then, if I take the bitset operations outside of the recursive function call, even with a bitset of size 400005, I get a memory usage of only 796KB!

Inside my recursive function, I am defining no new variables except a single long long and a single int — to my knowledge, combined with an absolute worst of 5000 function calls, this should only yield around 60KB of extra memory usage compared to a blank dfs. Obviously I am wrong. But I am confused — I am not declaring any new bitsets inside the recursive function, so why does the memory usage spike so high, and why does it depend on the size of the bitset?

If anybody understands why, I would be grateful for you to leave an explanation in the comments. Thanks