LeetCode Isomorphic Strings

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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// 08:18
class Solution {
public:
bool isIsomorphic(string s, string t) {
int slen = s.size();
int tlen = t.size();
if (slen != tlen) {
return false;
}
char tbl[256] = {0};
bool used[256] = {0};
for (int i=0; i<slen; i++) {
char ch = s[i];
if (tbl[ch] == 0 && !used[t[i]]) {
tbl[ch] = t[i];
used[t[i]] = true;
continue;
}
if (tbl[ch] != t[i]) {
return false;
}
}
return true;
}
};