Can anyone tell me what's going wrong with this recursive function?-CodePudding

So the question was to make a function that prints all permutations of a given string and stores them in an arraylist. My code was as follows:

import java.util.ArrayList;
class Solution
{
public static void permutations (String str, String perms, ArrayList<String> sets){
// base case
    if(str.length() == 0){
        sets.add(perms);
        return;
    } // end of base case

    for(int i =0; i<str.length(); i  ){
        char currentChar = str.charAt(i);
        String newStr = str.substring(0,i)  str.substring(i 1);
        permutations(newStr, perms currentChar, sets);
        return;
    }// end of for
} // end of permutations() function
public static void main(String args[]){
    ArrayList<String> sets = new ArrayList<>();
    permutations("ABC", "", sets);
    System.out.println(sets);
}// end of main 
}// end of class

The issue I'm facing is that the ArrayList is storing only the first variation; i.e, only ABC and none of the others. I've been trying to find out the error for quite a while but cannot find it. Would be glad if someone helps out :)

P.S. Here is a code that does not use an ArrayList to store the variations and directly prints them. This code is working as it should:

/*Q) recursive function to print all the permutations of a string*/
class Permutations{
public static void printPerms(String str, String permutation){
    // base case
    if(str.length()==0){
        System.out.println(permutation);
        return;
    }// end of base case

    for(int i = 0; i<str.length(); i  ){
        char currentChar = str.charAt(i);
        String newStr = str.substring(0,i)  str.substring(i 1);
        printPerms(newStr, permutation currentChar);
    } // end of for
} // end of printPerms

public static void main(String args[]){
    String str = "abc";
    printPerms(str, "");
  } // end of main()
}// end of class

CodePudding user response：

Return only need to be executed in base case when all the character in current iteration has been visited. But in your example, code is returning after calling printPerms function, so after processing 1 iteration for char at 0, it return and didn't processed any other character in string. Remove/comment return statement in for loop.

for(int i =0; i<str.length(); i  ){
    char currentChar = str.charAt(i);
    String newStr = str.substring(0,i)  str.substring(i 1);
    printPerms(newStr, perms currentChar, sets);
    //return;
}// end of for

CodePudding user response：

I found it. The issue is in the for loop. Your code contains return statement on the end of the loop. When I removed it, code is working.

for(int i =0; i<str.length(); i  ){
   char currentChar = str.charAt(i);
   String newStr = str.substring(0,i)  str.substring(i 1);
   permutations(newStr, perms currentChar, sets);
   return; // issue is in this line
}

Btw. my IDE shows me Dead code warning on i .