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

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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;
}

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