题目描述:

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.

依次建立替换的映射, 无法完成转换的条件有两个:

  1. s中两个不同的字符映射到了同一个字符. 用一个数组来记录每个字符是否被映射过, 出现重复时则返回false.
  2. s中的两个相同字符映射到不同字符. 每次比较字符的映射是否相同.
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class Solution {
public:
    bool isIsomorphic(string s, string t) {
        vector<int> s2t(128, -1), tCnt(128, 0);
        for(int i = 0; i < s.size(); i++){
            char sc = s[i], tc = t[i];
            if(s2t[sc] == -1){
                if(tCnt[tc] == 1) return false;
                s2t[sc] = tc;
                tCnt[tc] = 1;
            }
            else if(s2t[sc] != tc) return false;
        }
        return true;
    }
};