Given a string, check if all its characters are same or not.

Example 1:

Input:
s = "geeks"
Output: NO
Explanation: The string contains different
character 'g', 'e', 'k' and 's'.

​Example 2:

Input: 
s = "gggg"
Output: YES
Explanation: The string contains only one
character 'g'.

Your Task:
You don't need to read input or print anything. Your task is to complete the function check() which takes a string as input and returns true if all the characters in the string are same. Else, it returns false.

Expected Time Complexity: O(|S|).
Expected Auxiliary Space: O(1).

Constraints:
1 <= |S| <= 10⁴