Sum of zero sum series











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Given $n$ and $k$, I would like to know how to compute$$sum_{substack{x_0 ⊕x_1⊕cdots⊕x_k=0\x_i≥0, 0≤i≤k\sumlimits_{i=0}^kx_i≤n-2k}}binom{n-k-sumlimits_{i=0}^kx_i}k$$ in $O(nk·log n)$ time, where $⊕$ is exclusive or.










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  • This looks easy
    – David Peterson
    Nov 24 at 6:50










  • Could you please explain a little more?
    – Hang Wu
    Nov 24 at 9:15















up vote
0
down vote

favorite












Given $n$ and $k$, I would like to know how to compute$$sum_{substack{x_0 ⊕x_1⊕cdots⊕x_k=0\x_i≥0, 0≤i≤k\sumlimits_{i=0}^kx_i≤n-2k}}binom{n-k-sumlimits_{i=0}^kx_i}k$$ in $O(nk·log n)$ time, where $⊕$ is exclusive or.










share|cite|improve this question
























  • This looks easy
    – David Peterson
    Nov 24 at 6:50










  • Could you please explain a little more?
    – Hang Wu
    Nov 24 at 9:15













up vote
0
down vote

favorite









up vote
0
down vote

favorite











Given $n$ and $k$, I would like to know how to compute$$sum_{substack{x_0 ⊕x_1⊕cdots⊕x_k=0\x_i≥0, 0≤i≤k\sumlimits_{i=0}^kx_i≤n-2k}}binom{n-k-sumlimits_{i=0}^kx_i}k$$ in $O(nk·log n)$ time, where $⊕$ is exclusive or.










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Given $n$ and $k$, I would like to know how to compute$$sum_{substack{x_0 ⊕x_1⊕cdots⊕x_k=0\x_i≥0, 0≤i≤k\sumlimits_{i=0}^kx_i≤n-2k}}binom{n-k-sumlimits_{i=0}^kx_i}k$$ in $O(nk·log n)$ time, where $⊕$ is exclusive or.







combinatorics algorithms






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edited Nov 24 at 6:20









Saad

19.7k92252




19.7k92252










asked Nov 24 at 6:07









Hang Wu

404210




404210












  • This looks easy
    – David Peterson
    Nov 24 at 6:50










  • Could you please explain a little more?
    – Hang Wu
    Nov 24 at 9:15


















  • This looks easy
    – David Peterson
    Nov 24 at 6:50










  • Could you please explain a little more?
    – Hang Wu
    Nov 24 at 9:15
















This looks easy
– David Peterson
Nov 24 at 6:50




This looks easy
– David Peterson
Nov 24 at 6:50












Could you please explain a little more?
– Hang Wu
Nov 24 at 9:15




Could you please explain a little more?
– Hang Wu
Nov 24 at 9:15










1 Answer
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0
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I finally figure out an answer. This paper "Nim Fractals" by Tanya Khovanova and Joshua Xiong gives a recursive formula to count the solutions to $$begin{cases} x_0 oplus cdots oplus x_k =0 \sum_{i=0}^{k}x_i=Send{cases}$$ in $O(kS)$. Denote the number as $f(k,S)$. We may utilize $f$ to see that the problem reduces to $sum_{S=0}^{n-2k}binom{n-k-S}{k}f(k,S)$. The overall complexity is $O(nkcdot log(n))$.






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    1 Answer
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    1 Answer
    1






    active

    oldest

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    active

    oldest

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    active

    oldest

    votes








    up vote
    0
    down vote



    accepted










    I finally figure out an answer. This paper "Nim Fractals" by Tanya Khovanova and Joshua Xiong gives a recursive formula to count the solutions to $$begin{cases} x_0 oplus cdots oplus x_k =0 \sum_{i=0}^{k}x_i=Send{cases}$$ in $O(kS)$. Denote the number as $f(k,S)$. We may utilize $f$ to see that the problem reduces to $sum_{S=0}^{n-2k}binom{n-k-S}{k}f(k,S)$. The overall complexity is $O(nkcdot log(n))$.






    share|cite|improve this answer

























      up vote
      0
      down vote



      accepted










      I finally figure out an answer. This paper "Nim Fractals" by Tanya Khovanova and Joshua Xiong gives a recursive formula to count the solutions to $$begin{cases} x_0 oplus cdots oplus x_k =0 \sum_{i=0}^{k}x_i=Send{cases}$$ in $O(kS)$. Denote the number as $f(k,S)$. We may utilize $f$ to see that the problem reduces to $sum_{S=0}^{n-2k}binom{n-k-S}{k}f(k,S)$. The overall complexity is $O(nkcdot log(n))$.






      share|cite|improve this answer























        up vote
        0
        down vote



        accepted







        up vote
        0
        down vote



        accepted






        I finally figure out an answer. This paper "Nim Fractals" by Tanya Khovanova and Joshua Xiong gives a recursive formula to count the solutions to $$begin{cases} x_0 oplus cdots oplus x_k =0 \sum_{i=0}^{k}x_i=Send{cases}$$ in $O(kS)$. Denote the number as $f(k,S)$. We may utilize $f$ to see that the problem reduces to $sum_{S=0}^{n-2k}binom{n-k-S}{k}f(k,S)$. The overall complexity is $O(nkcdot log(n))$.






        share|cite|improve this answer












        I finally figure out an answer. This paper "Nim Fractals" by Tanya Khovanova and Joshua Xiong gives a recursive formula to count the solutions to $$begin{cases} x_0 oplus cdots oplus x_k =0 \sum_{i=0}^{k}x_i=Send{cases}$$ in $O(kS)$. Denote the number as $f(k,S)$. We may utilize $f$ to see that the problem reduces to $sum_{S=0}^{n-2k}binom{n-k-S}{k}f(k,S)$. The overall complexity is $O(nkcdot log(n))$.







        share|cite|improve this answer












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        share|cite|improve this answer










        answered Nov 29 at 4:32









        Hang Wu

        404210




        404210






























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