205. Isomorphic Strings (Map)

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.

思路: 注意本题是一一对应的关系，而hashmap只能保证索引值唯一，即s到t是唯一的，但是可能存在2个s对应同一个t，所以增加了set加以判断

class Solution {
public:
    bool isIsomorphic(string s, string t) {
        int len = s.length();
        if(len == 0) return true;

        map<char,char> c_map;
        set<char> c_set; //to avoid two character in s maps to the same character in t
        for(int i = 0; i < len; i++){
            if(c_map.find(s[i]) == c_map.end()){
                if(c_set.find(t[i]) == c_set.end()){
                    c_map[s[i]] = t[i];
                    c_set.insert(t[i]);
                }
                else return false;
            }
            else if(c_map[s[i]]!=t[i]) return false;
        }
        return true;
    }
};