{ "data": { "question": { "questionId": "730", "questionFrontendId": "730", "boundTopicId": null, "title": "Count Different Palindromic Subsequences", "titleSlug": "count-different-palindromic-subsequences", "content": "

Given a string s, return the number of different non-empty palindromic subsequences in s. Since the answer may be very large, return it modulo 109 + 7.

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A subsequence of a string is obtained by deleting zero or more characters from the string.

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A sequence is palindromic if it is equal to the sequence reversed.

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Two sequences a1, a2, ... and b1, b2, ... are different if there is some i for which ai != bi.

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Example 1:

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\nInput: s = "bccb"\nOutput: 6\nExplanation: The 6 different non-empty palindromic subsequences are 'b', 'c', 'bb', 'cc', 'bcb', 'bccb'.\nNote that 'bcb' is counted only once, even though it occurs twice.\n
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Example 2:

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\nInput: s = "abcdabcdabcdabcdabcdabcdabcdabcddcbadcbadcbadcbadcbadcbadcbadcba"\nOutput: 104860361\nExplanation: There are 3104860382 different non-empty palindromic subsequences, which is 104860361 modulo 109 + 7.\n
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Constraints:

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