题解 | 密码截取

st = input()  
length = len(st)  
maxlength = 1  # 最小的回文子串长度为1  
  
for i in range(length):  
    # 奇数长度的回文子串  
    l, r = i, i  
    while l >= 0 and r < length and st[l] == st[r]:  
        if r - l + 1 > maxlength:  
            maxlength = r - l + 1  
        l -= 1  
        r += 1  
  
    # 偶数长度的回文子串  
    l, r = i, i + 1  
    while l >= 0 and r < length and st[l] == st[r]:  
        if r - l + 1 > maxlength:  
            maxlength = r - l + 1  
        l -= 1  
        r += 1  
  
print(maxlength)