WHAT?

Guess what will happen tomorrow:

Yes

https://codeforces.me/blog/entry/93069

probably your not getting each answer fast enough

It's tricky — most implementations would be $$$O(K * combinations)$$$, which TLEs when K is close to N. You just have to do the combinations of $$$N-K$$$ elements in that case instead.

either k will be too small or k will be too large.
in the case of large k you have to choose $$$n - k$$$ elements which will not be included in sequence

61201371 Optimization in recursion:

• Stop if l<k
• if l==k then directly calculate with prefix xor.

Let $$$S$$$ be the set of all possible graph, $$$W(G)$$$ be cost of MST of $$$G$$$, $$$T_{\leq x}(G)$$$ be the minimum spanning forest form by edges in $$$G$$$ with weight $$$\leq x$$$, $$$w_e$$$ be the weight of an edge. Then we have

Then the problem reduced to sth similar to this problem, and can be solved by dp.

I solved A,B,D in 30 minutes, (skipped C) then I gazed at E for 15-20 minutes, without focusing on nCk <= 10^6. wasted 15-20 minutes for no reason.

What do you know about brutalness?

The data of D is so weak，damn!

61171841

The key insight for solving this problem lie sin the constraints. The total number of combinations must be less than 10^6. This allows you to design a solution that operates in O(K*10^6) where K is the size of your set.

1. Small k: K could be small, I think less than 16. So you can just generate all combinations and calculate xor sum.
2. Large K: K could be large, but then the complement N — K will be small, still less than 16. Flip the problem and solve for xor sum when you remove N — K elements from the set.