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.

维护两个哈希表。
第二个哈希表的功能就是保证不能有两个以上的字母映射到同一个字母。

class Solution {
public:
  bool isIsomorphic(string s, string t) {
        int table[256] = { 0 };
        int table2[256] = { 0 };
        string temp = "";
        for (int i = 0; i < s.size(); i++){
            if (table[s[i]] == 0){
                table[s[i]] = t[i];
            }
            if (table2[t[i]] == 0){
                table2[t[i]] = s[i];
            }
            else if (s[i] != table2[t[i]])
                return false;
            temp.push_back(table[s[i]]);
        }
        if (temp == t)
            return true;
        else
            return false;
    }
};