题目：

题解：

class Solution {public boolean isIsomorphic(String s, String t) {Map<Character, Character> s2t = new HashMap<Character, Character>();Map<Character, Character> t2s = new HashMap<Character, Character>();int len = s.length();for (int i = 0; i < len; ++i) {char x = s.charAt(i), y = t.charAt(i);if ((s2t.containsKey(x) && s2t.get(x) != y) || (t2s.containsKey(y) && t2s.get(y) != x)) {return false;}s2t.put(x, y);t2s.put(y, x);}return true;}
}