1153

class Solution {
public:
    bool canConvert(string s1, string s2) {
        if (s1 == s2) return true;
        unordered_map<char, char> dp;
        for (int i = 0; i < s1.length(); ++i) {
            if (dp[s1[i]] != NULL && dp[s1[i]] != s2[i])
                return false;
            dp[s1[i]] = s2[i];
        }
        return set(s2.begin(), s2.end()).size() < 26;
    }
};