LeetCode: Isomorphic Strings

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. 8 Given "paper", "title", return true.
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public class IsomorphicStrings {

    public boolean isIsomorphic(String s, String t) {
        if (s == null || t == null || s.length() != t.length()) {
            return false;
        }
        Map<Character, Character> map = new HashMap<Character, Character>();


        for (int i = 0; i < s.length(); i++) {
            char a = s.charAt(i);
            char b = t.charAt(i);

            if (map.containsKey(a)) {
                if (map.get(a) != b) {
                    return false;
                }
            } else {
                if (map.containsValue(b)) {
                    return false;
                }
                map.put(a, b);
            }
        }
        return true;
    }
}