[Swift]LeetCode1041. 困於環中的機器人 | Robot Bounded In Circle

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➤微信公衆號：山青詠芝（shanqingyongzhi）
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On an infinite plane, a robot initially stands at (0, 0) and faces north.  The robot can receive one of three instructions:

• "G": go straight 1 unit;
• "L": turn 90 degrees to the left;
• "R": turn 90 degress to the right.

The robot performs the instructions given in order, and repeats them forever.

Return true if and only if there exists a circle in the plane such that the robot never leaves the circle.

Example 1:

Input: "GGLLGG"
Output: true Explanation: The robot moves from (0,0) to (0,2), turns 180 degrees, and then returns to (0,0). When repeating these instructions, the robot remains in the circle of radius 2 centered at the origin. 

Example 2:

Input: "GG"
Output: false Explanation: The robot moves north indefinetely. 

Example 3:

Input: "GL"
Output: true Explanation: The robot moves from (0, 0) -> (0, 1) -> (-1, 1) -> (-1, 0) -> (0, 0) -> ...

Note:

1. 1 <= instructions.length <= 100
2. instructions[i] is in {'G', 'L', 'R'}

---

在無限的平面上，機器人最初位於 (0, 0) 處，面朝北方。機器人能夠接受下列三條指令之一：

• "G"：直走 1 個單位
• "L"：左轉 90 度
• "R"：右轉 90 度

機器人按順序執行指令 instructions，並一直重複它們。

只有在平面中存在環使得機器人永遠沒法離開時，返回 true。不然，返回 false。

示例 1：

輸入："GGLLGG"
輸出：true
解釋：
機器人從 (0,0) 移動到 (0,2)，轉 180 度，而後回到 (0,0)。
重複這些指令，機器人將保持在以原點爲中心，2 爲半徑的環中進行移動。

示例 2：

輸入："GG"
輸出：false
解釋：
機器人無限向北移動。

示例 3：

輸入："GL"
輸出：true
解釋：
機器人按 (0, 0) -> (0, 1) -> (-1, 1) -> (-1, 0) -> (0, 0) -> ... 進行移動。

提示：

1. 1 <= instructions.length <= 100
2. instructions[i] 在 {'G', 'L', 'R'} 中

---

0ms

 1 class Solution {
 2     enum dir {
 3         case px, py, nx, ny
 4         
 5         func turnL() -> dir
 6         {
 7             switch self {
 8             case .px: return .py
 9             case .py: return .nx
10             case .nx: return .ny
11             case .ny: return .px
12             }
13         }
14         
15         func trunR() -> dir
16         {
17             switch self {
18             case .px: return .ny
19             case .ny: return .nx
20             case .nx: return .py
21             case .py: return .px
22             }
23         }
24         
25         func move(point: inout [Int])
26         {
27             switch self {
28             case .px: point[0] += 1; return
29             case .py: point[1] += 1; return
30             case .nx: point[0] -= 1; return
31             case .ny: point[1] -= 1; return
32             }
33         }
34     }
35     
36     func isRobotBounded(_ instructions: String) -> Bool
37     {
38         if self.help(instructions) { return true }
39         else
40         {
41             var newInput = instructions
42             for _ in 1...3
43             {
44                 newInput.append(instructions)
45             }
46             return self.help(newInput)
47         }
48     }
49     
50     private func help(_ instructions: String) -> Bool
51     {
52         var d: dir = .px
53         // index0: x, index1: y
54         var p = [0,0]
55         
56         for c in instructions
57         {
58             if c == "G" { d.move(point: &p) }
59             else if c == "L" { d = d.turnL() }
60             else { d = d.trunR() }
61         }
62         
63         return p[0] == 0 && p[1] == 0
64     }
65 }

---

Runtime: 4 ms

Memory Usage: 20.5 MB

 1 class Solution {
 2     func isRobotBounded(_ instructions: String) -> Bool {
 3         let dx:[Int] = [0,-1,0,1]
 4         let dy:[Int] = [1,0,-1,0]
 5         let arr:[Character] = Array(instructions)
 6         var dir:Int = 0
 7         var x:Int = 0
 8         var y:Int = 0
 9         for i in 0..<arr.count
10         {
11             switch arr[i]
12             {
13                 case "L":
14                 dir += 1
15                 case "R":
16                 dir += 3
17                 default:
18                 x += dx[dir]
19                 y += dy[dir]
20             }
21             dir %= 4
22         }
23         return !((x != 0 || y != 0) && dir == 0)
24     }
25 }

---

Runtime: 8 ms

Memory Usage: 20.6 MB

 1 class Solution {
 2     func isRobotBounded(_ instructions: String) -> Bool {
 3         let dx:[Int] = [0,-1,0,1]
 4         let dy:[Int] = [1,0,-1,0]
 5         let arr:[Character] = Array(instructions)
 6         var dir:Int = 0
 7         var x:Int = 0
 8         var y:Int = 0
 9         for i in 0..<arr.count
10         {
11             switch arr[i]
12             {
13                 case "L":
14                 dir += 1
15                 case "R":
16                 dir += 3
17                 default:
18                 x += dx[dir]
19                 y += dy[dir]
20             }
21             dir %= 4
22         }
23         if dir != 0 {return true}
24         if x == 0 && y == 0 {return true}
25         return false
26     }
27 }

---

4ms

 1 class Solution {
 2     let directions = [(0, 1), (-1, 0), (0, -1), (1, 0)]
 3     func isRobotBounded(_ instructions: String) -> Bool {
 4 
 5         var index = 0
 6         var location = (0, 0)
 7         // for _ in 1...4 {
 8             location = getOnePass(instructions, location, &index)
 9         // }
10         return location.0 == 0 && location.1 == 0 || index > 0
11     }
12 
13     fileprivate func getOnePass(_ instructions: String, _ start: (Int, Int), _ index:inout Int) -> (Int, Int) {
14         
15         var curr = start
16         for item in instructions {
17             if item == "G" {
18                 curr = (curr.0 + directions[index].0, curr.1 + directions[index].1)
19             } else if item == "L" {
20                 index = (index + 3) % 4
21             } else if item == "R" {
22                 index = (index + 1) % 4
23             }
24         }
25         return curr
26     }
27 }