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| class Solution:
def longestPalindromeSubseq(self, s: str) -> int:
memo = [[[-1 for _ in range(27)] for _ in range(len(s))] for _ in range(len(s))]
def helper(i, j, prev):
if i >= j:
return 0
if memo[i][j][prev] != -1:
return memo[i][j][prev]
if ord(s[i]) - ord('a') == prev:
memo[i][j][prev] = helper(i + 1, j, prev)
elif ord(s[j]) - ord('a') == prev:
memo[i][j][prev] = helper(i, j - 1, prev)
elif s[i] == s[j]:
memo[i][j][prev] = helper(i + 1, j - 1, ord(s[i]) - ord('a')) + 2
else:
memo[i][j][prev] = max(
helper(i + 1, j, prev),
helper(i, j - 1, prev)
)
return memo[i][j][prev]
return helper(0, len(s) - 1, 26)
|