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.

public class Solution {
	/*
	 * 思路:利用一个Map来辅助解决问题，Map的key为s中的字符，Map的value为t中与之对应的字符
	 * 循环遍历s(题目中已经假设s和t长度相同), 
	 * 		如果遍历到的字符在Map中存在，则检测它对应的value
	 * 是否为t中对应的字符，是则继续，不是则直接返回false；
	 * 		如果遍历到的字符在Map中不存在，先检测Map的vlaue中是否包含t对应的字符，如果包含
	 * 直接返回false，如果不包含，则将s,t中对应的字符put进Map
	 * 
	 */
	public boolean isIsomorphic(String s, String t) {
		if (s==null || s.length()<=1) {
			return true;
		}
		Map<Character, Character> map = new HashMap<Character, Character>();
		for (int i=0; i<s.length(); i++) {
			Character a = s.charAt(i);
			Character b = t.charAt(i);
			if (map.containsKey(a)) {
				if (map.get(a).equals(b)) {
					continue;
				} else {
					return false;
				}
			} else {
				if (!map.containsValue(b)) {
					map.put(a, b);
				} else {
					return false;
				}
			}
		}
		return true;
	}
}