205. Isomorphic Strings

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.
Example 1:
Input: s = "egg", t = "add"
Output: true
Example 2:
Input: s = "foo", t = "bar"
Output: false
Example 3:
Input: s = "paper", t = "title"
Output: true
Note:
You may assume both s and t have the same length.



// correct

public boolean isIsomorphic(String s, String t) {
       char[] sc = s.toCharArray();
       char[] tc = t.toCharArray();
       int[] ms = new int[256];
       int[] mt = new int[256];
         Arrays.fill(ms, -1);
        Arrays.fill(mt, -1);
        
       for(int i =  0; i < sc.length; i++){
          int is = sc[i];
          int it = tc[i];
          if(ms[is] != mt[it]) return false;
          ms[is] = i;
          mt[it] = i; 
       }
        return true;
    }






// wrong 

class Solution {
    public boolean isIsomorphic(String s, String t) {
        if(s.length() != t.length()) return false;
        HashMap<Character, Character> map = new HashMap<>();
        
        for(int i = 0; i < s.length(); i++){
            char charS = s.charAt(i);
            char charT = t.charAt(i);
            if(!map.containsKey(charS)){
                if(!map.containsKey(charT)){
                    map.put(charS, charT);
                }else{
                    if(map.get(charT) != charS) return false;
                }
                
            }
            if(map.get(charS) != charT) return false;
        
        }
        return true;
        
    }
}
// Input:
// "ab"
// "aa"
// Output:
// true
// Expected:
// false



// still wrong result 
27 / 30 test cases passed.

class Solution {
    public boolean isIsomorphic(String s, String t) {
        if(s.length() != t.length()) return false;
        HashMap<Character, Character> map = new HashMap<>();
        for(int i = 0; i < s.length(); i++){
            char a = s.charAt(i);
            char b = t.charAt(i);
            if(!map.containsKey(a)){
                map.put(a, b);
            }
            if(!map.containsKey(b)){
                map.put(b, a);
            }
            if(map.containsKey(a)){
                if(b != map.get(a)) return false;
            }
            if(map.containsKey(b)){
                if(a != map.get(b)) return false;
            }
        }
        return true;   
    }
}


Input:
"ab"
"ca"
Output:
false
Expected:
true
    
    
a - > c 
c - > a 

b - > a 
a - > b  okay