题解 | #密码截取#

枚举每个位置，往两边扩散，分别考虑回文串长度是奇数和偶数的情况，最后取 即可。

originalStr = str(input())

maxLen = 0

for i in range(len(originalStr) - 1):
    if originalStr[i] == originalStr[i + 1]:    # 偶数长度回文子串
        start = i
        end = i + 1

        while start >= 0 and end < len(originalStr) and originalStr[start] == originalStr[end]:
            start -= 1
            end += 1
            maxLen = max(maxLen, end - start - 1)

    if originalStr[i - 1] == originalStr[i + 1]:    # 奇数长度回文子串
        start = i - 1
        end = i + 1

        while start >= 0 and end < len(originalStr) and originalStr[start] == originalStr[end]:
            start -= 1
            end += 1
            maxLen = max(maxLen, end - start - 1)

print(maxLen)