如何证明如果不是回文序列，删除两次就能删除所有字符？
class Solution:
def removePalindromeSub(self, s: str) -> int:
return 1 if s == s[::-1] else 2
#作者：LeetCode-Solution
#链接：https://leetcode-cn.com/problems/remove-palindromic-subsequences/solution/shan-chu-hui-wen-zi-xu-lie-by-leetcode-s-tqtb/
第n个字符的长度为2^n-1
n=1，k=0
n=2^n-1, k=1
(0, 2^n-1), k与Sn-1有关
(2^n-1), k为Sn-1取反，反转。
class Solution:
def findKthBit(self, n: int, k: int) -> str:
if k == 1:
return "0"
mid = 1 << (n - 1)
if k == mid:
return "1"
elif k < mid:
return self.findKthBit(n - 1, k)
else:
k = mid * 2 - k
return "0" if self.findKthBit(n - 1, k) == "1" else "1"
#作者：LeetCode-Solution
#链接：https://leetcode-cn.com/problems/find-kth-bit-in-nth-binary-string/solution/zhao-chu-di-n-ge-er-jin-zhi-zi-fu-chuan-zhong-de-2/
