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Unique Length 3 Palindromic Subsequences
MediumArraysCount the number of distinct length-3 palindromic subsequences in a string. A length-3 palindrome looks like x?x: the same character on both ends with any single character in the middle.
Input format (stdin): a single line, the string. Output the count of distinct such palindromes.
Examples
Input: aabca
Output: 3
aba, aaa, aca are the distinct palindromes.
Input: adc
Output: 0
No character repeats with something between.
Constraints
- 3 <= length <= 10^5
- lowercase English letters
Sheets
NeetCode 250
unique-length-3-palindromic-subsequences.cpp3 sample tests
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Custom input (stdin)
Output
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