King of the hill game












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$begingroup$


$k$ people start at $h=1$; if there are three people at height $t>0$, they compete and the winner goes up to $t+1$ while the two others go to $t-1$. Reaching height 0 results in the person being eliminated. If there are at most two people at any height, and the person/people at the highest height win. I'm trying to




  1. prove the game terminates/upper bound on number of competitions

  2. find how high up the top person will be

  3. prove that the order of competitions does not change the number of competitions at each height or how many people end up at each height


My reasoning so far:




  1. It seems that $phi(x_1,...,x_n)=sum_{i=1}^n$ decreases by one each time there is a competition meaning that it will eventually reach zero -- I'm not sure how to make this a proper proof (induction?)


  2. I'm guessing the height has something to do with $log_3$ as it takes three people to advance one of the people one.


  3. I don't know how to formalize the idea that a person can only advance once two others join him, so he will "wait", which is what leads to the invariant.











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$endgroup$












  • $begingroup$
    I don't understand this. Suppose there are $7$ people at height $1$ to begin with. How many competitions take place in the first round?
    $endgroup$
    – saulspatz
    Jan 16 at 1:50










  • $begingroup$
    @saulspatz in the first round, two competitions would take place
    $endgroup$
    – faeophyta
    Jan 16 at 20:09
















0












$begingroup$


$k$ people start at $h=1$; if there are three people at height $t>0$, they compete and the winner goes up to $t+1$ while the two others go to $t-1$. Reaching height 0 results in the person being eliminated. If there are at most two people at any height, and the person/people at the highest height win. I'm trying to




  1. prove the game terminates/upper bound on number of competitions

  2. find how high up the top person will be

  3. prove that the order of competitions does not change the number of competitions at each height or how many people end up at each height


My reasoning so far:




  1. It seems that $phi(x_1,...,x_n)=sum_{i=1}^n$ decreases by one each time there is a competition meaning that it will eventually reach zero -- I'm not sure how to make this a proper proof (induction?)


  2. I'm guessing the height has something to do with $log_3$ as it takes three people to advance one of the people one.


  3. I don't know how to formalize the idea that a person can only advance once two others join him, so he will "wait", which is what leads to the invariant.











share|cite|improve this question









$endgroup$












  • $begingroup$
    I don't understand this. Suppose there are $7$ people at height $1$ to begin with. How many competitions take place in the first round?
    $endgroup$
    – saulspatz
    Jan 16 at 1:50










  • $begingroup$
    @saulspatz in the first round, two competitions would take place
    $endgroup$
    – faeophyta
    Jan 16 at 20:09














0












0








0


1



$begingroup$


$k$ people start at $h=1$; if there are three people at height $t>0$, they compete and the winner goes up to $t+1$ while the two others go to $t-1$. Reaching height 0 results in the person being eliminated. If there are at most two people at any height, and the person/people at the highest height win. I'm trying to




  1. prove the game terminates/upper bound on number of competitions

  2. find how high up the top person will be

  3. prove that the order of competitions does not change the number of competitions at each height or how many people end up at each height


My reasoning so far:




  1. It seems that $phi(x_1,...,x_n)=sum_{i=1}^n$ decreases by one each time there is a competition meaning that it will eventually reach zero -- I'm not sure how to make this a proper proof (induction?)


  2. I'm guessing the height has something to do with $log_3$ as it takes three people to advance one of the people one.


  3. I don't know how to formalize the idea that a person can only advance once two others join him, so he will "wait", which is what leads to the invariant.











share|cite|improve this question









$endgroup$




$k$ people start at $h=1$; if there are three people at height $t>0$, they compete and the winner goes up to $t+1$ while the two others go to $t-1$. Reaching height 0 results in the person being eliminated. If there are at most two people at any height, and the person/people at the highest height win. I'm trying to




  1. prove the game terminates/upper bound on number of competitions

  2. find how high up the top person will be

  3. prove that the order of competitions does not change the number of competitions at each height or how many people end up at each height


My reasoning so far:




  1. It seems that $phi(x_1,...,x_n)=sum_{i=1}^n$ decreases by one each time there is a competition meaning that it will eventually reach zero -- I'm not sure how to make this a proper proof (induction?)


  2. I'm guessing the height has something to do with $log_3$ as it takes three people to advance one of the people one.


  3. I don't know how to formalize the idea that a person can only advance once two others join him, so he will "wait", which is what leads to the invariant.








proof-writing algorithms






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asked Jan 16 at 1:24









faeophytafaeophyta

104




104












  • $begingroup$
    I don't understand this. Suppose there are $7$ people at height $1$ to begin with. How many competitions take place in the first round?
    $endgroup$
    – saulspatz
    Jan 16 at 1:50










  • $begingroup$
    @saulspatz in the first round, two competitions would take place
    $endgroup$
    – faeophyta
    Jan 16 at 20:09


















  • $begingroup$
    I don't understand this. Suppose there are $7$ people at height $1$ to begin with. How many competitions take place in the first round?
    $endgroup$
    – saulspatz
    Jan 16 at 1:50










  • $begingroup$
    @saulspatz in the first round, two competitions would take place
    $endgroup$
    – faeophyta
    Jan 16 at 20:09
















$begingroup$
I don't understand this. Suppose there are $7$ people at height $1$ to begin with. How many competitions take place in the first round?
$endgroup$
– saulspatz
Jan 16 at 1:50




$begingroup$
I don't understand this. Suppose there are $7$ people at height $1$ to begin with. How many competitions take place in the first round?
$endgroup$
– saulspatz
Jan 16 at 1:50












$begingroup$
@saulspatz in the first round, two competitions would take place
$endgroup$
– faeophyta
Jan 16 at 20:09




$begingroup$
@saulspatz in the first round, two competitions would take place
$endgroup$
– faeophyta
Jan 16 at 20:09










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