_205.java

package com.fishercoder.solutions;

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

public class _205 {
    /**
     * space should be O(1) since it only has alphabetic letters which are capped at 52.
     */

    public static class Solution1 {
        public boolean isIsomorphic(String s, String t) {
            if (s == null || s.length() == 0) {
                return (t == null || t.length() == 0);
            }
            if (t == null || t.length() == 0) {
                return (s == null || s.length() == 0);
            }
            char[] schar = s.toCharArray();
            char[] tchar = t.toCharArray();
            Map<Character, Character> map = new HashMap();
            if (s.length() != t.length()) {
                return false;
            }
            for (int i = 0; i < s.length(); i++) {
                if (map.containsKey(schar[i])) {
                    if (map.get(schar[i]) != tchar[i]) {
                        return false;
                    }
                } else {
                    if (map.containsValue(tchar[i])) {
                        return false;//this line is necessary for this case: ("ab", "aa")
                    }
                    map.put(schar[i], tchar[i]);
                }
            }
            return true;
        }
    }
}