Strings Homomorphism

题目：

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.

 注意事项

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

您在真实的面试中是否遇到过这个题？ 

Yes

样例

Given s = "egg", t = "add", return true.

Given s = "foo", t = "bar", return false.

Given s = "paper", t = "title", return true.

思路：

建立一个s到t的映射来判断，接着再建立t到s的映射判断。

代码：

class Solution {
public:
    /**
     * @param s a string
     * @param t a string
     * @return true if the characters in s
     * can be replaced to get t or false
     */
    bool isIsomorphic(string& s, string& t) {
        // Write your code here
        if(s.length()!=t.length())
            return false;
        map<char,char>a;
        for(int i=0;i<s.length();i++)
        { if(a.find(s[i])==a.end()) a[s[i]]=t[i];
          else if(a[s[i]]!=t[i]) return false;
        }
        a.clear();
        for(int i=0;i<t.length();i++)
        { if(a.find(t[i])==a.end()) a[t[i]]=s[i];
          else if(a[t[i]]!=s[i]) return false;
        }
        return true;
        
    }
};

感想：原来这道题我是写的s到t的，没有写t到s的映射，然后就过不了，后来才注意到有特殊情况，就改了。