Consider a recursive function called permuteR $($string$,$ position$)$ that returns each reordering of the letters in a string.

def swap$(st,1,r)$ :

$st=$ list$($st$)$

$st[1],st[r]=st[r],$st$[1]$

return $\text{'}\text{'}.$join$($st$)$

def permuteR$($st$,l=0$ :

if len$(st)==1$ :

return $[$st$]$

$L=[]$

for $i$ in range$(1,$ len$($st$))$:

st $=$swap$(st,i,1)$

L $+=$ permuteR$($st$,$ l$+1)$

st $=$swap$(st,i,1)$

return $L$

print$($permuteR$("123"))$

# $[\text{'}123\text{'},\text{'}132\text{'},\text{'}213\text{'},\text{'}231\text{'},\text{'}321\text{'},\text{'}312\text{'}]$

Which of the following statements is TRUE about permuteR?

None of other selections are valid

permuteR is tail recursive

permuteR is not tail recursive but can be modified to be tail recursive

permuteR is not tail recursive