Intuition

In order to determine if two strings are isomorphic, you can check if you can replace every occurrence of the letter s in one string with the corresponding letter t in the other string, and vice versa. In other words, there should be a one-to-one mapping between the characters of the two strings.

Approach

Let's consider the strings egg and add. We can replace e with a, g with d, and the resulting strings are add and add. Similarly, if we take and bar, there is no consistent mapping that allows us to replace characters, so these strings are not isomorphic.

Complexity

• Time complexity: O(n)

• Space complexity: O(n)

Code

class Solution {
public:
 bool isIsomorphic(string s, string t) {
    unordered_map<char,char> mp, mp2;
    for(int i=0; i<s.size(); i++){
        if(mp[s[i]] && mp[s[i]]!=t[i]) return false;
        if(mp2[t[i]] && mp2[t[i]]!=s[i]) return false;
        mp[s[i]] = t[i];
        mp2[t[i]] = s[i];
    }   
    return true;
 }
};