leetcode-205. 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.

代码

public boolean isIsomorphic(String s, String t) {
        if (s == null || t == null || s.length() != s.length()) {
            return false;
        }
        HashMap<Character,Character> m1 = new HashMap<Character,Character>();
        HashMap<Character,Character> m2 = new HashMap<Character,Character>();
        for (int i = 0; i < s.length(); i++) {
            if (!m1.containsKey(s.charAt(i))) {
                if (m2.containsKey(t.charAt(i))) return false;
                m1.put(s.charAt(i), t.charAt(i));
                m2.put(t.charAt(i), s.charAt(i));
            } else {
                if (m1.get(s.charAt(i)) != t.charAt(i)) return false;
            }
        }
        return true;
    }

leetcode-205. isomorphic strings

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