Word Pattern

Word Pattern
Given a  pattern  and a string  str , find if  str  follows the same pattern.
Here follow means a full match, such that there is a bijection between a letter in  pattern  and a non-empty word in  str .
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: You may assume  pattern  contains only lowercase letters, and  str  contains lowercase letters separated by a single space.
Credits: Special thanks to @minglotus6 for adding this problem and creating all test cases.
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class Solution {
public:
    bool wordPattern(string pattern, string str) {
        auto i = 1;
        string tmp,tmp_str;
        istringstream is(str);
        is>>tmp_str;
        if(tmp_str==""&&pattern[0]=='\0')return true;
        if(tmp_str==""&&pattern[0]!='\0')return false;
        while(is>>tmp!=""){
             if(pattern[i]=='\0')
            return false;
            if(pattern[i]==patterm[i-1]){
                if(tmp != tmp_str)
                return false;
            }
            else{
                if(tmp == tmp_str)
                return false;
            }
           
            tmp_str = tmp;
            ++i;
        }
        if(pattern[i]!='\0')return false;
        
        return true;
        
    }
    
};