Given a string s, find the longest palindromic subsequence's length in s.
A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements.
Example 1:
Input: s = "bbbab"
Output: 4
Explanation: One possible longest palindromic subsequence is "bbbb".
Example 2:
Input: s = "cbbd"
Output: 2
Explanation: One possible longest palindromic subsequence is "bb".
Constraints:
-
1 <= s.length <= 1000 -
sconsists only of lowercase English letters.
SOLUTION:
class Solution:
cache = {}
def maxPalindrome(self, s, i, j):
key = 1100 * i + j
if (key) in self.cache:
return self.cache[key]
if i == j:
self.cache[key] = 1
elif s[i] == s[j] and i + 1 == j:
self.cache[key] = 2
elif s[i] == s[j]:
self.cache[key] = self.maxPalindrome(s, i + 1, j - 1) + 2
else:
self.cache[key] = max(self.maxPalindrome(s, i, j - 1), self.maxPalindrome(s, i + 1, j))
return self.cache[key]
def longestPalindromeSubseq(self, s: str) -> int:
self.cache.clear()
return self.maxPalindrome(s, 0, len(s) - 1)
Top comments (0)