Java Program to Find All the Permutations of a String

One fascinating problem in the world of strings is the generation of permutations. In essence, a permutation of a string is any arrangement of its characters in a different sequence. For instance, the permutations of the string "abc" are "abc", "acb", "bac", "bca", "cab", and "cba". In this article, we will write a Java program that generates all permutations of a given string. 

The Strategy

• We'll approach this problem recursively. 
• Choose each character as a starting character and find permutations of the remaining characters.
• Recursively repeat the process for the remaining characters until no characters are left. 

Java Program to Find All the Permutations of a String

public class StringPermutations {

    public static void main(String[] args) {
        String input = "abc";
        generatePermutations(input, "");
        System.out.println("All permutations of " + input + " have been displayed.");
    }

    public static void generatePermutations(String str, String ans) {
        if (str.length() == 0) {
            System.out.println(ans);
            return;
        }

        for (int i = 0; i < str.length(); i++) {
            char ch = str.charAt(i);
            String remaining = str.substring(0, i) + str.substring(i + 1);
            generatePermutations(remaining, ans + ch);
        }
    }
}

Output:

abc
acb
bac
bca
cab
cba
All permutations of abc have been displayed.

Step by Step Explanation: 

Setting Up the String:

        String input = "abc";

We initialized a string named input which we want to generate permutations for. 

Base Case:

        if (str.length() == 0) {
            System.out.println(ans);
            return;
        }

Our recursive function, generatePermutations, will work by picking characters from str and adding them to ans. The base case is when str becomes empty, meaning we have formed a permutation in ans, which we then print. 

Recursive Permutations Generation: 

        for (int i = 0; i < str.length(); i++) {
            char ch = str.charAt(i);
            String remaining = str.substring(0, i) + str.substring(i + 1);
            generatePermutations(remaining, ans + ch);
        }

This loop traverses through each character in the string. For every character: 

• We pick it out (denoted by ch). 
• Generate a new string remaining which is the original string minus the picked character. 
• We call our function recursively with this new string, adding our chosen character to the ans string.

Recursive Magic: 

This process will keep repeating until every character has been the starting character, and we've explored all possible combinations of the remaining characters.

Conclusion

Generating permutations of a string is a classic example of a problem that can be elegantly and efficiently solved using recursion. This beginner's guide provides a clear pathway to understanding and implementing this solution in Java. Remember, recursion can initially feel a little tricky, but with practice, its patterns and beauty will become evident.

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