205. Isomorphic Strings

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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.

Solution

 public boolean isIsomorphic(String s, String t) {
        //use array to record the index of each character
        int m1[] = new int[256];
        int m2[] = new int[256];
        for(int i = 0; i < s.length(); i++){
            //Check if the charaters with same index appear in same index before
            //if not, it means the charater has appeared in other index, then it is not
            //isomorphic
            if(m1[s.charAt(i)] != m2[t.charAt(i)]) return false;
                
            //use i+1 to avoid intial condition 0, cause the misjudement    
            m1[s.charAt(i)] = i + 1;
            m2[t.charAt(i)] = i + 1;
        }
        return true;
    }