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45 lines
1.2 KiB
Python
45 lines
1.2 KiB
Python
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"""
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author: Sanket Kittad
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Given a string s, find the longest palindromic subsequence's length in s.
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Input: s = "bbbab"
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Output: 4
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Explanation: One possible longest palindromic subsequence is "bbbb".
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Leetcode link: https://leetcode.com/problems/longest-palindromic-subsequence/description/
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"""
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def longest_palindromic_subsequence(input_string: str) -> int:
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"""
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This function returns the longest palindromic subsequence in a string
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>>> longest_palindromic_subsequence("bbbab")
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4
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>>> longest_palindromic_subsequence("bbabcbcab")
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7
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"""
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n = len(input_string)
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rev = input_string[::-1]
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m = len(rev)
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dp = [[-1] * (m + 1) for i in range(n + 1)]
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for i in range(n + 1):
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dp[i][0] = 0
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for i in range(m + 1):
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dp[0][i] = 0
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# create and initialise dp array
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for i in range(1, n + 1):
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for j in range(1, m + 1):
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# If characters at i and j are the same
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# include them in the palindromic subsequence
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if input_string[i - 1] == rev[j - 1]:
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dp[i][j] = 1 + dp[i - 1][j - 1]
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else:
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dp[i][j] = max(dp[i - 1][j], dp[i][j - 1])
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return dp[n][m]
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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