```
class Solution {
public:
bool isIsomorphic(string s, string t) {
int s2n[256]={0}, t2n[256]={0};
for(int i=0; i<s.size(); i++){
if(s2n[s[i]]>0||t2n[t[i]]>0){
if(s2n[s[i]]==t2n[t[i]]) continue;
else return false;
}
else{
s2n[s[i]]=i+1;//map char s[i] to location of s[i] in s, should be the same mapping of t[i] to location t[i] in t
t2n[t[i]]=i+1;
}
}
return true;
}
};
```