leetcode 205. Isomorphic Strings

題目

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

public class Solution {
      public boolean isIsomorphic(String s, String t) {

        if(s==null && t==null) 
            return true;    
        if(s==null|| t==null) 
            return false;
        if(s.length()!=t.length()) 
            return false;

        Map<Character,Character> map=new HashMap<Character,Character>();
        Set<Character> set=new HashSet<Character>();

        for(int i=0;i<s.length();i++){
            char c1=s.charAt(i);
            char c2=t.charAt(i);

            if(map.containsKey(c1)){//包含在映射中
                if(map.get(c1)!=c2)
                    return false;
            }else{
                if(set.contains(c2)){
                //不包含在映射中，但是已經該值已經被其他鍵對應過，
                //屬於多對一的情況
                    return false;
                }else{
                    map.put(c1, c2);
                    set.add(c2);
                }       
            }
        }

        return true;

    }
}

參考鏈接

http://blog.csdn.net/xudli/article/details/45386777
http://blog.csdn.net/DERRANTCM/article/details/48021425