# 205-isomorphic-strings

## Question

https://leetcode.com/problems/isomorphic-strings/description/

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.

Example:

``````Given "egg", "add", return true.

Given "foo", "bar", return false.

Given "paper", "title", return true.
``````

## Thought Process

1. Hash Table and Boolean
1. Use hashtable to track the mapping of characters and boolean to track whether a character has been used already
2. Time complexity O(n)
3. Space complexity O(1)

## Solution

``````class Solution {
public boolean isIsomorphic(String s, String t) {
if (s.length() != t.length()) return false;
char[] map = new char[256];
boolean[] used = new boolean[256];
char[] sc = s.toCharArray();
char[] tc = t.toCharArray();
for (int i = 0; i < sc.length; i++) {
// if this character has not been mapped
if (map[sc[i]] == 0) {
if (used[tc[i]]) return false;
map[sc[i]] = tc[i];
used[tc[i]] = true;
} else if (map[sc[i]] != tc[i]) {
return false;
}
}
return true;
}
}
``````