[LeetCode-JAVA] Isomorphic Strings

题目：

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.

思路：终于又出个简单的了，读完题就能看到，用map保存映射，同时还要判断value是否被映射过，用set进行过滤

代码：

public class Solution {
    public boolean isIsomorphic(String s, String t) {
        Map<Character, Character> map = new HashMap<Character, Character>();
        Set<Character> set = new HashSet<Character>();
        StringBuilder sb = new StringBuilder();
        for(int i = 0 ; i < len ; i++){
            if(!map.containsKey(s.charAt(i))){
                if(!set.contains(t.charAt(i))){  //过滤 value t
                    map.put(s.charAt(i), t.charAt(i));  // s -> t
                    set.add(t.charAt(i));
                }
                else
                    return false;
            }
            sb.append(map.get(s.charAt(i)));    
        }
        return sb.toString().equals(t);
    }
}