字符串/hashtable——leetcode205

205. Isomorphic Strings

问题描述：

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.

解析：

字符串同构问题，重点是字符映射。
同一位置上的字符相互映射

public boolean isIsomorphic(String s, String t) {
       if(s==null || s.length()<=1)
			return true;
		HashMap<Character,Character> hm=new HashMap<Character,Character>();
		for(int i=0;i<s.length();i++){
			char ch1=s.charAt(i);
			char ch2=t.charAt(i);
			if(hm.containsKey(ch1)){
				if(hm.get(ch1)==ch2)
					continue;
				else
					return false;
			}else{
				if(hm.containsValue(ch2))
					return false;
				else
					hm.put(ch1, ch2);
			}
		}
		return true;
    }