[Swift]LeetCode1227. 飞机座位分配概率 | Airplane Seat Assignment Probability

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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

有 n 位乘客即将登机，飞机正好有 n 个座位。第一位乘客的票丢了，他随便选了一个座位坐下。

剩下的乘客将会：

如果他们自己的座位还空着，就坐到自己的座位上，

当他们自己的座位被占用时，随机选择其他座位
第 n 位乘客坐在自己的座位上的概率是多少？

示例 1：

输入：n = 1
输出：1.00000
解释：第一个人只会坐在自己的位置上。
示例 2：

输入: n = 2
输出: 0.50000
解释：在第一个人选好座位坐下后，第二个人坐在自己的座位上的概率是 0.5。

提示：

1 <= n <= 10^5

Runtime: 4 ms

Memory Usage: 21.1 MB

 1 class Solution {
 2     func nthPersonGetsNthSeat(_ n: Int) -> Double {
 3         if n == 1
 4         {
 5             return 1.0
 6         }
 7         else
 8         {
 9             return 0.5
10         }
11     }
12 }