leetcode | Word Pattern

Given a  pattern  and a string  str , find if  str  follows the same pattern.
Examples:
pattern =  "abba" , str =  "dog cat cat dog"  should return true.
pattern =  "abba" , str =  "dog cat cat fish"  should return false.
pattern =  "aaaa" , str =  "dog cat cat dog"  should return false.
pattern =  "abba" , str =  "dog dog dog dog"  should return false.
Notes:
Both  pattern  and  str  contains only lowercase alphabetical letters.
Both  pattern  and  str  do not have leading or trailing spaces.
Each word in  str  is separated by a single space.
Each letter in  pattern  must map to a word with length that is at least 1.

public class Solution {
    public boolean wordPattern(String pattern, String str) {
            String[] s = str.split(" ");
            if(s.length!=pattern.length())  return false;
            Map<Character,String> map = new HashMap<Character,String>();
            for(int i=0;i<pattern.length();i++)
            {
                if(!map.containsKey(pattern.charAt(i)))
                {
                    if(map.containsValue(s[i]))
                        return false;
                    map.put(pattern.charAt(i),s[i]);
                }
                else
                {
                    if(!map.get(pattern.charAt(i)).equals(s[i]))
                        return false;
                }
            }
            return true;
        }
}