[Swift]LeetCode672. 灯泡开关 Ⅱ | Bulb Switcher II

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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].

---

现有一个房间，墙上挂有 n 只已经打开的灯泡和 4 个按钮。在进行了 m 次未知操作后，你需要返回这 n 只灯泡可能有多少种不同的状态。

假设这 n 只灯泡被编号为 [1, 2, 3 ..., n]，这 4 个按钮的功能如下：

1. 将所有灯泡的状态反转（即开变为关，关变为开）
2. 将编号为偶数的灯泡的状态反转
3. 将编号为奇数的灯泡的状态反转
4. 将编号为 3k+1 的灯泡的状态反转（k = 0, 1, 2, ...)

示例 1:

输入: n = 1, m = 1.
输出: 2
说明: 状态为: [开], [关]

示例 2:

输入: n = 2, m = 1.
输出: 3
说明: 状态为: [开, 关], [关, 开], [关, 关]

示例 3:

输入: n = 3, m = 1.
输出: 4
说明: 状态为: [关, 开, 关], [开, 关, 开], [关, 关, 关], [关, 开, 开].

注意： n 和 m 都属于 [0, 1000].

---

Runtime: 4 ms

Memory Usage: 18.9 MB

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

---

4ms

class Solution {
    struct State: Hashable, OptionSet {
        let rawValue: Int

        static let oddSensitive = State(rawValue: 1)
        static let evenInsensitive = State(rawValue: 2)
        static let oddInsensitive = State(rawValue: 4)
        static let evenSensitive = State(rawValue: 8)
        
        static let odd: State = [.oddSensitive, .oddInsensitive]
        static let even: State = [.evenSensitive, .evenInsensitive]
        static let sensitive: State = [.evenSensitive, .oddSensitive]
        
        static let all: State = [.oddSensitive, .oddInsensitive, .evenSensitive, .evenInsensitive]
    }
    
    func flipLights(_ n: Int, _ m: Int) -> Int {
        let mask = State(rawValue: 1 << min(n, 4) - 1)
        let permittedCount = Set<Int>(0...4).filter { $0 <= m && ($0 % 2) == (m % 2) }

        var states = Set<State>()
        
        for i in 0..<16 {
            var count = 0, state = State.all
            if (i & 1) != 0 {
                state.formSymmetricDifference(.all)
                count += 1
            }
            if (i & 2) != 0 {
                state.formSymmetricDifference(.even)
                count += 1
            }
            if (i & 4) != 0 {
                state.formSymmetricDifference(.odd)
                count += 1
            }
            if (i & 8) != 0 {
                state.formSymmetricDifference(.sensitive)
                count += 1
            }
            
            if permittedCount.contains(count) {
                states.insert(state.intersection(mask))
            }
        }
        
        return states.count
    }
}