Isomorphic.java

//Program to check whether two strings s and t are isomorphic or not
//Two strings are isomorphic if the characters in s can be replaced to get t
//for example, "egg" and "add" are isomorphic but "foo" and "bar" are not

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Isomorphic {
    static boolean isIsomorphic(String s,String t)
    {
        if(s==null || t==null)
            return false;

        if(s.length()!=t.length())
            return false;

        if(s.length()==0 && t.length()==0)
            return true;

        HashMap<Character,Character> map = new HashMap<>();
        for(int i=0;i<s.length();i++)
        {
            char c1=s.charAt(i);
            char c2=t.charAt(i);

            Character c = getKey(map,c2);
            if(c!=null && c!=c1) {
                return false;
            }
            else if(map.containsKey(c1)) {
                if(c2!=map.get(c1))
                    return false;
            }
            else {
                map.put(c1,c2);
            }
        }
        return true;
    }

    static Character getKey(HashMap<Character,Character> map, Character target)
    {
        for(Map.Entry<Character,Character> entry : map.entrySet())
        {
            if(entry.getValue().equals(target))
                return entry.getKey();
        }
        return null;
    }

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        System.out.println("Enter Two Strings: ");
        String s1=sc.next();
        String s2 = sc.next();
        if(isIsomorphic(s1,s2))
            System.out.println("Strings are isomorphic");
        else
            System.out.println("Strings are not isomorphic");
    }
}