题解 | #密码截取# （最长对称连续子串）
密码截取
http://www.nowcoder.com/practice/3cd4621963e8454594f00199f4536bb1
分最长对称子串的长度是奇数（k）还是偶数（l）处理。
ss = input()
l,i = 2,0 # l=2n
while (0<=i) and (i< len(ss)-l+1):
if ss[i:i+l] == ss[i:i+l][::-1]:
l += 2
i -= 2 if i > 0 else 1 # avoid i back to -1
i += 1
k,i = 3,0 # k=2n+1
while (0<=i) and (i< len(ss)-k+1):
if ss[i:i+k] == ss[i:i+k][::-1]:
k += 2
i -= 2 if i > 0 else 1 # avoid i back to -1
i += 1
print(max(k,l)-2)