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

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➤微信公眾號：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。機器人可以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，並一直重復它們。

只有在平面中存在環使得機器人永遠無法離開時，返回 true。否則，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，然后回到 (0,0)。
重復這些指令，機器人將保持在以原點為中心，2 為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

class Solution {
    enum dir {
        case px, py, nx, ny
        
        func turnL() -> dir
        {
            switch self {
            case .px: return .py
            case .py: return .nx
            case .nx: return .ny
            case .ny: return .px
            }
        }
        
        func trunR() -> dir
        {
            switch self {
            case .px: return .ny
            case .ny: return .nx
            case .nx: return .py
            case .py: return .px
            }
        }
        
        func move(point: inout [Int])
        {
            switch self {
            case .px: point[0] += 1; return
            case .py: point[1] += 1; return
            case .nx: point[0] -= 1; return
            case .ny: point[1] -= 1; return
            }
        }
    }
    
    func isRobotBounded(_ instructions: String) -> Bool
    {
        if self.help(instructions) { return true }
        else
        {
            var newInput = instructions
            for _ in 1...3
            {
                newInput.append(instructions)
            }
            return self.help(newInput)
        }
    }
    
    private func help(_ instructions: String) -> Bool
    {
        var d: dir = .px
        // index0: x, index1: y
        var p = [0,0]
        
        for c in instructions
        {
            if c == "G" { d.move(point: &p) }
            else if c == "L" { d = d.turnL() }
            else { d = d.trunR() }
        }
        
        return p[0] == 0 && p[1] == 0
    }
}

---

Runtime: 4 ms

Memory Usage: 20.5 MB

class Solution {
    func isRobotBounded(_ instructions: String) -> Bool {
        let dx:[Int] = [0,-1,0,1]
        let dy:[Int] = [1,0,-1,0]
        let arr:[Character] = Array(instructions)
        var dir:Int = 0
        var x:Int = 0
        var y:Int = 0
        for i in 0..<arr.count
        {
            switch arr[i]
            {
                case "L":
                dir += 1
                case "R":
                dir += 3
                default:
                x += dx[dir]
                y += dy[dir]
            }
            dir %= 4
        }
        return !((x != 0 || y != 0) && dir == 0)
    }
}

---

Runtime: 8 ms

Memory Usage: 20.6 MB

class Solution {
    func isRobotBounded(_ instructions: String) -> Bool {
        let dx:[Int] = [0,-1,0,1]
        let dy:[Int] = [1,0,-1,0]
        let arr:[Character] = Array(instructions)
        var dir:Int = 0
        var x:Int = 0
        var y:Int = 0
        for i in 0..<arr.count
        {
            switch arr[i]
            {
                case "L":
                dir += 1
                case "R":
                dir += 3
                default:
                x += dx[dir]
                y += dy[dir]
            }
            dir %= 4
        }
        if dir != 0 {return true}
        if x == 0 && y == 0 {return true}
        return false
    }
}

---

4ms

class Solution {
    let directions = [(0, 1), (-1, 0), (0, -1), (1, 0)]
    func isRobotBounded(_ instructions: String) -> Bool {

        var index = 0
        var location = (0, 0)
        // for _ in 1...4 {
            location = getOnePass(instructions, location, &index)
        // }
        return location.0 == 0 && location.1 == 0 || index > 0
    }

    fileprivate func getOnePass(_ instructions: String, _ start: (Int, Int), _ index:inout Int) -> (Int, Int) {
        
        var curr = start
        for item in instructions {
            if item == "G" {
                curr = (curr.0 + directions[index].0, curr.1 + directions[index].1)
            } else if item == "L" {
                index = (index + 3) % 4
            } else if item == "R" {
                index = (index + 1) % 4
            }
        }
        return curr
    }
}