Josephus Problem

Question

100 people standing in a circle in an order 1 to 100. No. 1 has a sword. He kills the next person (i.e. No. 2) and gives the sword to the next (i.e. No. 3). All people do the same until only 1 survives. Which number survives at the last? There are 100 people starting from 1 to 100. 
 can anyone please tell me how can i do it?

Chris · Accepted Answer

This is my example with a recursive rule to solve the puzzle (#73). 
 As always, make sure to save recursive rules before testing. 
 /* rule!chris_test_kc_recur(
 list (Number Array, 1+enumerate(100))
 index (Number, 1)
 )
*/

if(
 count(ri!list)<=1,
 index(ri!list,1,null),
 a!localVariables(
 local!removeIndex: if(
 ri!index=count(ri!list),
 1,
 if(
 ri!index>count(ri!list),
 2,
 ri!index+1
 )
 ),
 local!list: remove(ri!list,local!removeIndex),
 rule!chris_test_kc_recur(
 list: local!list,
 index: local!removeIndex
 )
 )
)

Nikhil Tetali · Answer

Here is the solution to your challenge. We have also added a feather so that the user may choose the number of players and who should start the game. 
 reduce(
 rule!EI_subEliminateTask(list: _, value: _),
 {
 ldrop(
 enumerate(ri!players) + 1,
 ri!startPlayer - 1
 ),
 if(
 ri!startPlayer = 1,
 {},
 enumerate(ri!startPlayer - 1) + 1
 )
 },
 repeat(ri!players - 1, 0)
)

subrule: rule!EI_subEliminateTask(list: _, value: _),
code: { ldrop(ri!list, 2), ri!list[1] }

Josephus Problem

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