题解 | 密码截取

import sys

s = input()
n = len(s)

dp = [[0 for _ in range(n)] for _ in range(n)]
max_len = 1
for i in range(n-1, -1, -1):
    for j in range(i, n):
        if s[i] == s[j] and (j-i < 3 or dp[i+1][j-1]):
            dp[i][j] = 1
            max_len = max(max_len, j-i+1)
print(max_len)