【leetcode】1227. Airplane Seat Assignment Probability

题目如下：

n passengers board an airplane with exactly n seats. The first passenger has lost the ticket and picks a seat randomly. But after that, the rest of passengers will:

• Take their own seat if it is still available, 
• Pick other seats randomly when they find their seat occupied 

What is the probability that the n-th person can get his own seat?

Example 1:

Input: n = 1
Output: 1.00000
Explanation: The first person can only get the first seat.

Example 2:

Input: n = 2
Output: 0.50000
Explanation: The second person has a probability of 0.5 to get the second seat (when first person gets the first seat).

Constraints:

• 1 <= n <= 10^5

解题思路：我计算了n=3，4，5时的概率，发现都是0.5，所以就有了一个大胆的猜想，除了n=1之外，其他的概率都是0.5。

代码如下：

class Solution(object):
    def nthPersonGetsNthSeat(self, n):
        """
        :type n: int
        :rtype: float
        """
        if n == 1 : return float(1)
        return 0.50000