标签:Binary 1545 String invert bs Input Output Example reverse
题目如下:
Given two positive integers
n
andk
, the binary stringSn
is formed as follows:
S1 = "0"
Si = Si-1 + "1" + reverse(invert(Si-1))
fori > 1
Where
+
denotes the concatenation operation,reverse(x)
returns the reversed string x, andinvert(x)
inverts all the bits in x (0 changes to 1 and 1 changes to 0).For example, the first 4 strings in the above sequence are:
S1 = "0"
S2 = "011"
S3 = "0111001"
S4 = "011100110110001"
Return the
kth
bit inSn
. It is guaranteed thatk
is valid for the givenn
.Example 1:
Input: n = 3, k = 1 Output: "0" Explanation: S3 is "0111001". The first bit is "0".Example 2:
Input: n = 4, k = 11 Output: "1" Explanation: S4 is "011100110110001". The 11th bit is "1".Example 3:
Input: n = 1, k = 1 Output: "0"Example 4:
Input: n = 2, k = 3 Output: "1"Constraints:
1 <= n <= 20
1 <= k <= 2n - 1
解题思路:n最大才20,把Sn算出来都行。
代码如下:
class Solution(object): def findKthBit(self, n, k): """ :type n: int :type k: int :rtype: str """ bs = '0' def reverse_invert(input): output = '' for i in input: output += '1' if i == '0' else '0' return output[::-1] for i in range(1,n+1): bs = bs + '1' + reverse_invert(bs) return bs[k-1]
标签:Binary,1545,String,invert,bs,Input,Output,Example,reverse 来源: https://www.cnblogs.com/seyjs/p/14351538.html
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