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Complementary Pairs of Strings

Two strings form a complementary pair if there exists some permutation of their concatenation that forms a palindrome. For example, the strings 'abc' and 'cab' form a complementary pair since their concatenation 'abccab' can be rearranged to form the palindrome 'abcba'. Given an array of strings, find the number of complementary pairs that can be formed. Note that pairs (i, j) and (j, i) are considered the same.

Example 1:

Input:[["ball","all","call","ball"]]

Output:3

Example 2:

Input:[["eye","aa","c"]]

Output:2

Constraints:

1 ≤ n ≤ 10^5
1 ≤ length(stringData[i]) ≤ 3 * 10^5
1 ≤ sum of the length of strings in stringData ≤ 3 * 10^5

solution.cpp

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Complementary Pairs of Strings

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Two strings form a complementary pair if there exists some permutation of their concatenation that forms a palindrome. For example, the strings 'abc' and 'cab' form a complementary pair since their concatenation 'abccab' can be rearranged to form the palindrome 'abcba'. Given an array of strings, find the number of complementary pairs that can be formed. Note that pairs (i, j) and (j, i) are considered the same.