Linkedin Interview - Isomorphic Strings

Given two strings, determine if they are isomorphic. 

Two words are called isomorphic if the letters in one word can be remapped to get the second word. Remapping a letter means replacing all occurrences of it with another letter while the ordering of the letters remains unchanged. No two letters may map to the same letter, but a letter may map to itself.

Examples: 

Given 'foo', 'app', returns true
We can map 'f' -> 'a' and 'o' -> 'p'

Given 'bar', 'foo', returns false
We can’t map both 'a' and 'r' to 'o'

Given 'turtle', 'tletur', returns true
We can map 't' -> 't', 'u' -> 'l', 'r' -> 'e', 'l' -> 'u', 'e' -'r'

Given 'ab', 'ca', returns true
We can map 'a' -> 'c', 'b' -> 'a'

public boolean is_isomorphic(String s, String t) {
    if(s.length() != t.length()) return false;
    Map<Character, Character> mapS = new HashMap<>(), 
    mapT = new HashMap<>();
    
    for(int i=0; i<s.length(); i++) {
        char cs = s.charAt(i);
        char ct = t.charAt(i);
        if(!mapS.containsKey(cs)) {
            mapS.put(cs, ct);
        } else if(mapS.get(cs) != ct) {
            return false;
        }
        
        if(!mapT.containsKey(ct)) {
            mapT.put(ct, cs);
        } else if(mapT.get(ct) != cs) {
            return false;
        }
    }
    return true;
}