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Count the number of distinct non-empty palindromic subsequences in a string (n ≤ 1000, alphabet {a,b,c,d}), returning the result modulo 1e9+7. The core challenge is using interval dynamic programming with careful deduplication of subsequences to avoid overcounting repeated characters.
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Salesforce
Leetcode 730. Count Different Palindromic Subsequences
Reported May 3, 2025 · 1 source report
SENIOR
Source snapshot: Nov 12, 2026
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