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.

For example,
Given "egg", "add", return true.

Given "foo", "bar", return false.

Given "paper", "title", return true.

Solution:

class Solution {
public:
    bool isIsomorphic(string s, string t) {
        map<char, char> map, map2;
        int size = s.size(), size2 = t.size();
        if (size != size2)
            return false;
        for (int i = 0; i < size; i++) {
            if (map.find(s[i]) == map.end()) {
                map[s[i]] = t[i];
            } else if (map[s[i]] != t[i]) {
                return false;
            }
            if (map2.find(t[i]) == map2.end()) {
                map2[t[i]] = s[i];
            } else if (map2[t[i]] != s[i]) {
                return false;
            }
        }
        return true;
    }
};