Given two strings s and t, determine if they are isomorphic.
Two strings s and t 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.
Example 1:
Input:s = "egg", t = "add"
Output:true
Explanation:
The strings s and t can be made identical by:
Mapping 'e' to 'a'.
Mapping 'g' to 'd'.
Example 2:
Input:s = "foo", t = "bar"
Output:false
Explanation:
The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'.
Example 3:
Input:s = "paper", t = "title"
Output:true
Constraints:
1 <= s.length <= 5 * 104
t.length == s.length
s and t consist of any valid ascii character.
Solutions
Solution 1: Hash Table or Array
We can use two hash tables or arrays $d_1$ and $d_2$ to record the character mapping relationship between $s$ and $t$.
Traverse $s$ and $t$, if the corresponding character mapping relationships in $d_1$ and $d_2$ are different, return false, otherwise update the corresponding character mapping relationships in $d_1$ and $d_2$. After the traversal is complete, it means that $s$ and $t$ are isomorphic, and return true.
The time complexity is $O(n)$ and the space complexity is $O(C)$. Where $n$ is the length of the string $s$; and $C$ is the size of the character set, which is $C = 256$ in this problem.