Integer listSize is read from input, then listSize strings are read from input and stored in ArrayList airportsToPick. The recursive method generateAllRoutes$()$ explores all possible routes defined by a source and a destination picked from airportsToPick. In generateAllRoutes$(),$ write the base case to output the following items if the size of ArrayList pickedAirports is $2$:

"Depart: $"$

first element in pickedAirports

$",$ Arrive: $"$

second element in pickedAirports

End with a newline.

Click here for example

Note: ArrayList input always has at least $2$ elements.

import java.util.Scanner;

import java.util.ArrayList;

public class Routes $\{$

public static void generateAllRoutes$($ArrayList remainAirports, ArrayList pickedAirports$)\{$

int i;

String pick;

$/*$ Your code goes here $*/$

else $\{$

for $($i $=0$; i $<$ remainAirports.size$()$; $++$i$)\{$

pick $=$ remainAirports.get$($i$)$;

remainAirports.remove$($i$)$;

pickedAirports.add$($pick$)$;

generateAllRoutes$($remainAirports$,$ pickedAirports$)$;

remainAirports.add$($i$,$ pick$)$;

pickedAirports.remove$($pickedAirports$.$size$()-1)$;

$\}$

$\}$

$\}$

public static void main$($String$[]$ args$)\{$

Scanner scnr $=$ new Scanner$($System$.$in$)$;

ArrayList airportsToPick $=$ new ArrayList$()$;

ArrayList picks $=$ new ArrayList$()$;

int listSize;

int i;

listSize $=$ scnr$.$nextInt$()$;

for $($i $=0$; i $<$ listSize; $++$i$)\{$

airportsToPick.add$($scnr$.$next$())$;

$\}$

System.out.println$("$All possible routes:"$)$;

generateAllRoutes$($airportsToPick$,$ picks$)$;

$\}$

$\}$