LeetCode:Isomorphic Strings

问题描述：

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.

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思路：

这道题是判断两个单词是否同构。这里的同构的意思是，对于例子egg和add，若存在一个映射，e->a，g->d，单词egg和add同构。注意，不可以多个字符映射到同一个字符中去，比如aa和ab。因此要有两个hash表来记录。由于是字符，不会超过256个，因此可以用数组来记录这种映射。

代码：

class Solution {
public:
    bool isIsomorphic(string s, string t) {
        if(s.length() != t.length())  return false;
        char charmap1[256];
        char charmap2[256];
        memset(charmap1,0,sizeof(char) * 256);
        memset(charmap2,0,sizeof(char) * 256);

        for(int i = 0; i < s.length();++i){
            if(charmap1[s[i]] == 0){
                charmap1[s[i]] = t[i] ;
            }
            else if(charmap1[s[i]] != t[i]){
                return  false;
            }
             if(charmap2[t[i]] == 0){
                charmap2[t[i]] = s[i] ;
            }
            else if(charmap2[t[i]] != s[i]){
                return  false;
            }
        }
       return true;
    }
};