[Swift]LeetCode672. 燈泡開關 Ⅱ | Bulb Switcher II

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➤微信公衆號：山青詠芝（shanqingyongzhi）
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There is a room with n lights which are turned on initially and 4 buttons on the wall. After performing exactly munknown operations towards buttons, you need to return how many different kinds of status of the n lights could be.

Suppose n lights are labeled as number [1, 2, 3 ..., n], function of these 4 buttons are given below:

1. Flip all the lights.
2. Flip lights with even numbers.
3. Flip lights with odd numbers.
4. Flip lights with (3k + 1) numbers, k = 0, 1, 2, ... 

Example 1:

Input: n = 1, m = 1.
Output: 2
Explanation: Status can be: [on], [off] 

Example 2:

Input: n = 2, m = 1.
Output: 3
Explanation: Status can be: [on, off], [off, on], [off, off] 

Example 3:

Input: n = 3, m = 1.
Output: 4
Explanation: Status can be: [off, on, off], [on, off, on], [off, off, off], [off, on, on]. 

Note: n and m both fit in range [0, 1000].

---

現有一個房間，牆上掛有 n 只已經打開的燈泡和 4 個按鈕。在進行了 m 次未知操做後，你須要返回這 n 只燈泡可能有多少種不一樣的狀態。

假設這 n 只燈泡被編號爲 [1, 2, 3 ..., n]，這 4 個按鈕的功能以下：

1. 將全部燈泡的狀態反轉（即開變爲關，關變爲開）
2. 將編號爲偶數的燈泡的狀態反轉
3. 將編號爲奇數的燈泡的狀態反轉
4. 將編號爲 3k+1 的燈泡的狀態反轉（k = 0, 1, 2, ...)

示例 1:

輸入: n = 1, m = 1.
輸出: 2
說明: 狀態爲: [開], [關]

示例 2:

輸入: n = 2, m = 1.
輸出: 3
說明: 狀態爲: [開, 關], [關, 開], [關, 關]

示例 3:

輸入: n = 3, m = 1.
輸出: 4
說明: 狀態爲: [關, 開, 關], [開, 關, 開], [關, 關, 關], [關, 開, 開].

注意： n 和 m 都屬於 [0, 1000].

---

Runtime: 4 ms

Memory Usage: 18.9 MB

1 class Solution {
2     func flipLights(_ n: Int, _ m: Int) -> Int {
3         var n = min(n, 3)
4         return min(1 << n, 1 + m * n)
5     }
6 }

---

4ms

 1 class Solution {
 2     struct State: Hashable, OptionSet {
 3         let rawValue: Int
 4 
 5         static let oddSensitive = State(rawValue: 1)
 6         static let evenInsensitive = State(rawValue: 2)
 7         static let oddInsensitive = State(rawValue: 4)
 8         static let evenSensitive = State(rawValue: 8)
 9         
10         static let odd: State = [.oddSensitive, .oddInsensitive]
11         static let even: State = [.evenSensitive, .evenInsensitive]
12         static let sensitive: State = [.evenSensitive, .oddSensitive]
13         
14         static let all: State = [.oddSensitive, .oddInsensitive, .evenSensitive, .evenInsensitive]
15     }
16     
17     func flipLights(_ n: Int, _ m: Int) -> Int {
18         let mask = State(rawValue: 1 << min(n, 4) - 1)
19         let permittedCount = Set<Int>(0...4).filter { $0 <= m && ($0 % 2) == (m % 2) }
20 
21         var states = Set<State>()
22         
23         for i in 0..<16 {
24             var count = 0, state = State.all
25             if (i & 1) != 0 {
26                 state.formSymmetricDifference(.all)
27                 count += 1
28             }
29             if (i & 2) != 0 {
30                 state.formSymmetricDifference(.even)
31                 count += 1
32             }
33             if (i & 4) != 0 {
34                 state.formSymmetricDifference(.odd)
35                 count += 1
36             }
37             if (i & 8) != 0 {
38                 state.formSymmetricDifference(.sensitive)
39                 count += 1
40             }
41             
42             if permittedCount.contains(count) {
43                 states.insert(state.intersection(mask))
44             }
45         }
46         
47         return states.count
48     }
49 }