同构字符串 Isomorphic Strings

Problem

Given two (dictionary) words as Strings, determine if they are isomorphic.

Two words are called isomorphic if the letters in one word can be remapped to get the second word.

Remapping a letter means replacing all occurrences of it with another letter while the ordering of the letters remains unchanged.

No two letters may map to the same letter, but a letter may map to itself.

 Example:

given "foo", "app"; returns true we can map f -> a and o->p
given "bar", "foo"; returns false we can't map both 'a' and 'r' to 'o'

given "ab", "ca"; returns true we can map 'a' -> 'b' and 'c' -> 'a'

最直接的方法就是见两个HashMap维护住字符的对应关系，O(n)

public static boolean check(String s,String t){
		if(s.length()!=t.length()) return false;
		HashMap<Character,Character> map1=new HashMap<Character, Character>();
		HashMap<Character,Character> map2=new HashMap<Character, Character>();
		
		for(int i=0;i<s.length();i++){
			char c1=s.charAt(i);
			char c2=t.charAt(i);
			if(map1.containsKey(c1)){
				if(map1.get(c1)!=c2) return false;
			}
			if(map2.containsKey(c2)){
				if(map2.get(c2)!=c1) return false;
			}
			
			map1.put(c1, c2);
			map2.put(c2, c1);
		}
		return true;
	}