Given a string, find the number of pairs of characters that are same. Pairs (s[i], s[j]), (s[j], s[i]), (s[i], s[i]), (s[j], s[j]) should be considered different.
Example 1:
Input:
S = "air"
Output: 3
Explanation: 3 pairs that are equal:
(S[0], S[0]), (S[1], S[1]) and (S[2], S[2])
​Example 2:
Input:
S = "aa"
Output: 4
Explanation: 4 pairs that are equal:
(S[0], S[0]), (S[0], S[1]), (S[1], S[0])
and (S[1], S[1])
Your Task:
You don't need to read input or print anything. Your task is to complete the function equalPairs() which takes the string S as input and returns the number of equal pairs as described in the problem description.
Expected Time Complexity: O(|S|). Expected Auxiliary Space: O(1).
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Avoid using static/global variables in coding problems as your code is tested
against multiple test cases and these tend to retain their previous values.
Passing the Sample/Custom Test cases in coding problems does not guarantee the
correctness of code. On submission, your code is tested against multiple test cases
consisting of all possible corner cases and stress constraints.
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