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.

Note:You may assume both s and t have the same length.

class Solution {
public:
    void feature(string &s, map<char, vector<int> >& m){
        for(int i=0;i<s.size();i++){
            if(m.count(s[i]) == 0){
                vector<int> v = vector<int>();
                v.push_back(i);
                m[s[i]] = v;
            }else{
                m[s[i]].push_back(i);
            }
        }
    }
    
    bool compare(map<char, vector<int> >m, vector<int> diff){
        for (std::map<char,vector<int> >::iterator it=m.begin(); it!=m.end(); ++it){
            vector<int> &v = it->second;
            if(v.size() > 0){
                for(int i=1;i<v.size();i++){
                    if(diff[v[0]] != diff[v[i]])
                        return false;
                }
            }
        }
        return true;
    }
    bool isIsomorphic(string s, string t) {
        // You may assume both s and t have the same length.
        if(s.size() == 0) return true; 
        
        map<char, vector<int> >ms = map<char, vector<int> >();
        map<char, vector<int> >mt = map<char, vector<int> >();
        vector<int> diff = vector<int>();
        
        feature(s, ms);
        feature(t, mt);
        for(int i=0;i<s.size();i++){
            diff.push_back(s[i] - t[i]);
        }
        
        return compare(ms, diff) && compare(mt, diff);
    }
};