bhaag_milkha's blog

By bhaag_milkha, history, 10 months ago, In English

Can some one help me on how to solve this problem?

Editorial is given in Japanese, i used google translater to understand it but some sentence doesn't make any sense to me and i couldn't understand solution from editorial.

 
 
 
 
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10 months ago, # |
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Problem tag — Digit DP.

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10 months ago, # |
Rev. 2   Vote: I like it +11 Vote: I do not like it

Here is my submission, which you can refer to: Atcoder Submission 8567969

I don't know the solution of the editorial, just give it on my own.

Prerequesite knowledge: For every $$$a, b \in \mathbb{N}$$$ then $$$a+b = a\oplus b + 2\times (a\ and\ b) =(a\ or\ b) + (a\ and\ b)$$$. Well this is easy to prove.

Therefore let $$$x = a\ or\ b,\ y = a\ and\ b,\ u = a\oplus b,\ v = a+b$$$ then $$$x+y = v, x-y = u$$$. So for each pair $$$(u, v)$$$ in the answer maps with exactly one pair $$$(x, y)$$$, and each pair $$$(x, y)$$$ such that $$$y \subseteq x, y \le x \le N$$$ corresponds with only one pair $$$(u, v)$$$. Here $$$y \subseteq x$$$ means in binary representation, each bit of $$$y$$$ is smaller than the corresponding bit of $$$x$$$.

So we can count the number of pair $$$(a, b)$$$ such that $$$b \subseteq a, a+b \le N$$$.

Let say in binary representation, $$$a = \overline{a_{60}a_{59}...a_{1}a_{0}}$$$ and $$$b = \overline{b_{60}b_{59}...b_{1}b_{0}}$$$ then we can solve the problem using Digit DP. You can refer to my solution.

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    10 months ago, # ^ |
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    Thanks a lot for your explanation

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    8 months ago, # ^ |
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    i'm newbie to CP and didn't understand your explaination could u please elaborate how we can count the no. of pairs (x,y) such that y⊆x,y≤x≤N given that N <= 10^18 it will not pass the time limit.

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    6 months ago, # ^ |
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    Hi

    Can someone explain the dp required to count pairs of (a,b) described above?

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10 months ago, # |
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