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.


You may assume both s and t have the same length.




// Isomorphic Strings
// Time Complexity: O(n), Space Complexity: O(n)
public class Solution {
    public boolean isIsomorphic(String s, String t) {
        if (s.length() != t.length()) return false;

        final Map<Character,Character> map1 = new HashMap<>();
        final Map<Character,Character> map2 = new HashMap<>();

        for (int  i = 0; i < s.length(); ++i) {
            final char c1 = s.charAt(i);
            final char c2 = t.charAt(i);

            if (map1.containsKey(c1)) {
                if (map1.get(c1) != c2) return false;
            } else {
                map1.put(c1, c2);

            if (map2.containsKey(c2)) {
                if (map2.get(c2) != c1) return false;
            } else {
                map2.put(c2, c1);
        return true;


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