IsomorphicStrings.java

package string;

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

/**
 * Created by gouthamvidyapradhan on 11/04/2018.
 * Given two strings s and t, determine if they are isomorphic.

 Two strings are isomorphic if the characters in s can be replaced to get t.

 All occurrences of a character must be replaced with another character while preserving the order of characters. No
 two characters may map to the same character but a character may map to itself.

 For example,
 Given "egg", "add", return true.

 Given "foo", "bar", return false.

 Given "paper", "title", return true.

 Note:
 You may assume both s and t have the same length.
 Solution O(N): Maintain two hashmaps and compare character by character.
 */
public class IsomorphicStrings {
    /**
     * Main method
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception{
        System.out.println(new IsomorphicStrings().isIsomorphic("abc", "dea"));
    }

    public boolean isIsomorphic(String s, String t) {
        if(s.length() != t.length()) return false;
        Map<Character, Character> first = new HashMap<>();
        Map<Character, Character> second = new HashMap<>();
        for(int i = 0; i < s.length(); i ++){
            char c = s.charAt(i);
            if(first.containsKey(c)){
                char secondC = first.get(c);
                if(t.charAt(i) != secondC) return false;
            } else{
                first.put(c, t.charAt(i));
                if(second.containsKey(t.charAt(i))) return false;
                second.put(t.charAt(i), c);
            }
        }
        return true;
    }

}