Josephus problem: Difference between revisions

Line 3,527:

*The idiomatic way to roll an array in R (e.g. as [[Josephus_problem#Ruby|the Ruby solution]] has) is to exploit the head and tail functions, but those break if we are rolling by more than the length of the array (see https://stackoverflow.com/q/18791212 for a few tricks for this).

Regardless, it is still solvable. The following adapts a great deal of [[Josephus_problem#Lua|the Lua solution]]. The arguments n, k, and m are as in the task description.

<lang rsplus>josephusProblem<-function(n,k,m)

<lang rsplus>josephusProblem <- function(n, k, m)

{

prisoners<-0:(n-1)

prisoners <- 0:(n - 1)

exPos<-countToK<-1

exPos <- countToK <- 1

dead<-integer(0)

dead <- integer(0)

while(length(prisoners)>m)

while(length(prisoners) > m)

{

if(countToK==k)

if(countToK == k)

{

dead<-c(dead,prisoners[exPos])

dead <- c(dead, prisoners[exPos])

prisoners<-prisoners[-exPos]

prisoners <- prisoners[-exPos]

exPos<-exPos-1

exPos <- exPos - 1

}

exPos<-exPos+1

exPos <- exPos + 1

countToK<-countToK+1

countToK <- countToK + 1

if(exPos>length(prisoners)){exPos<-1}

if(exPos > length(prisoners)) exPos <- 1

if(countToK>k){countToK<-1}

if(countToK > k) countToK <- 1

}

print(paste0("Execution order: ",paste0(dead,collapse =", "),"."))

print(paste0("Execution order: ", paste0(dead, collapse = ", "), "."))

paste0("Survivors: ",paste0(prisoners,collapse =", "),".")

paste0("Survivors: ", paste0(prisoners, collapse = ", "), ".")

}</lang>

<pre>> josephusProblem(5,2,1)

<pre>> josephusProblem(5, 2, 1)

[1] "Execution order: 1, 3, 0, 4."

[1] "Survivors: 2."

> josephusProblem(41,3,1)

> josephusProblem(41, 3, 1)

[1] "Execution order: 2, 5, 8, 11, 14, 17, 20, 23, 26, 29, 32, 35, 38, 0, 4, 9, 13, 18, 22, 27, 31, 36, 40, 6, 12, 19, 25, 33, 39, 7, 16, 28, 37, 10, 24, 1, 21, 3, 34, 15."

[1] "Survivors: 30."

> josephusProblem(41,3,3)

> josephusProblem(41, 3, 3)

[1] "Execution order: 2, 5, 8, 11, 14, 17, 20, 23, 26, 29, 32, 35, 38, 0, 4, 9, 13, 18, 22, 27, 31, 36, 40, 6, 12, 19, 25, 33, 39, 7, 16, 28, 37, 10, 24, 1, 21, 3."

[1] "Survivors: 15, 30, 34."</pre>