Check if a two character string can be made using given words

Given a string of two characters and n distinct words of two characters. The task is to find if it is possible to arrange given words in such a way that the concatenated string has the given two character string as a substring. We can append a word multiple times.

Examples: 

Input : str = "ya"
        words[] = {"ah", "oy", "to", "ha"} 
Output : YES
We can join "oy" and then "ah", and
then "ha" to form the string "oyahha" 
which contains the string "ya".
 So, the answer is "YES"

Input : str[] = "ha"
        words[] = "ah"
Output :YES
The string "ahah" contains "ha" 
as a substring.

Input : str = "hp"
       words[] = {"ht", "tp"|
Output :NO
We can't produce a string containing
"hp" as a sub-string. Note that we
can join "ht" and then "tp" producing
"http", but it doesn't contain the 
"hp" as a sub-string.

If we look at the given examples carefully, we can see that our answer will be “YES” if any of the following conditions is true, 

1. str is equal to any one of the N words
2. str is equal to reverse of any of the words.
3. It first letter of str is equal to last letter of any of the given N strings and last letter is equal to the first letter of any of the given N strings.

Otherwise our output will always be NO.

Below is the implementation of the above approach.

Output

Yes

Time Complexity: O(n), where n represents the size of the given vector.
Auxiliary Space: O(1), no extra space is required, so it is a constant.