LeetCode Problem #205 : Isomorphic Strings

Given two strings s and t, determine if they are isomorphic. Two strings s and t 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

My thought:

This required a bit of thinking, we couldnt use sorting, and strings cannot be isomorphic if they are of different length. the n i wrote the first conditional line to return false; then I thought that there is mapping regarding items between s and t so I added hashmap and did the mapping then tried to run, but failed at the condition similar to: “badc” “baba”

here d is new, but its mapped to b, which should already be mapped to itself. so i added second hashmap to save the ReverseMapping. and checking both the mapping for false condition. and voila it passed.

I saw some solutions using array which are much efficient than what I wrote. but having 41.06 MB (Beats 91% is enough for me.)

Initial Solution:

    class Solution {
    public boolean isIsomorphic(String s, String t) {
        if(s.length() != t.length()) return false;
        char[] sc = s.toCharArray();
        char[] tc = t.toCharArray();
        HashMap<Character,Character> map = new HashMap<>();
        HashMap<Character,Character> reversemap = new HashMap<>();
        for(int i=0;i< s.length();i++){
            if(map.containsKey(sc[i]) && map.get(sc[i])!=tc[i]) return false;
            else map.put(sc[i],tc[i]);

            if(reversemap.containsKey(tc[i]) && reversemap.get(tc[i])!=sc[i]) return false;
            else reversemap.put(tc[i],sc[i]);
        }
        return true;
    }
}

Peformance:

N/A