Given a string s consisting of uppercase and lowercase alphabetic characters. Return the number of distinct substrings of size 2 that appear in s as contiguous substrings.
Example
Input :
s = "ABCAB"
Output :
3
Explanation: For "ABCAB", the
three distinct substrings of size
2 are "AB", "BC" and "CA".
Example
Input :
s = "XYZ"
Output :
2
Explanation: For "XYZ", the
two distinct substrings of size 2 are
"XY" and "YZ".
Your Task :
You don't need to read input or print anything. You have to complete the function fun() which takes the string s as input parameter and returns the number of distinct contiguous substring of size 2.
Expected Time Complexity : O(|s|)
Expected Auxilliary Space : O(|s|)
Constraints:
1<=|s|<=100
|s| denotes the length of the string s.

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