[Swift]LeetCode130. 被围绕的区域 | Surrounded Regions

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Given a 2D board containing 'X' and 'O' (the letter O), capture all regions surrounded by 'X'.

A region is captured by flipping all 'O's into 'X's in that surrounded region.

Example:

X X X X
X O O X
X X O X
X O X X

After running your function, the board should be:

X X X X
X X X X
X X X X
X O X X

Explanation:

Surrounded regions shouldn’t be on the border, which means that any 'O' on the border of the board are not flipped to 'X'. Any 'O' that is not on the border and it is not connected to an 'O' on the border will be flipped to 'X'. Two cells are connected if they are adjacent cells connected horizontally or vertically.

---

 给定一个二维的矩阵，包含 'X' 和 'O'（字母 O）。

找到所有被 'X' 围绕的区域，并将这些区域里所有的 'O' 用 'X' 填充。

示例:

X X X X
X O O X
X X O X
X O X X

运行你的函数后，矩阵变为：

X X X X
X X X X
X X X X
X O X X

解释:

被围绕的区间不会存在于边界上，换句话说，任何边界上的 'O' 都不会被填充为 'X'。 任何不在边界上，或不与边界上的 'O' 相连的 'O' 最终都会被填充为 'X'。如果两个元素在水平或垂直方向相邻，则称它们是“相连”的。

---

52ms

class Solution {
    func solve(_ board: inout [[Character]]) {
        let h = board.count
        guard h > 2 else { return }
        
        let w = board[0].count
        guard w > 2 else { return }
        
        for i in 0..<h {
            mark(&board, i, 0)
            mark(&board, i, w - 1)
        }
        
        for j in 0..<w {
            mark(&board, 0, j)
            mark(&board, h - 1, j)
        }
        
        for i in 0..<h {
            for j in 0..<w {
                if board[i][j] == "O" {
                   board[i][j] = "X"
                } else if board[i][j] == "T" {
                   board[i][j] = "O"
                }
            }
        }
    }
    
    func mark(_ board: inout [[Character]], _ i: Int, _ j: Int) {
        guard i >= 0 && i < board.count else { return }
        guard j >= 0 && j < board[i].count else { return }
        guard board[i][j] == "O" else { return }
        
        board[i][j] = "T"
        
        mark(&board, i - 1, j)
        mark(&board, i + 1, j)
        mark(&board, i, j - 1)
        mark(&board, i, j + 1)
    }
}

---

56ms

class Solution {
    func solve(_ board: inout [[Character]]) {
        for i in 0..<board.count {
            for j in 0..<board[i].count {
                if (i == 0 || i == board.count - 1 || j == 0 || j == board[i].count - 1) && board[i][j] == "O" {
                    dfs(&board, i, j)
                }

            }
        }
        for i in 0..<board.count {
            for j in 0..<board[i].count {
                if board[i][j] == "O" {
                    board[i][j] = "X"
                }
                if board[i][j] == "Y" {
                    board[i][j] = "O"
                }
            }
        }
    }
    private func dfs(_ board: inout [[Character]], _ i: Int, _ j: Int) {
        if board[i][j] == "O" {

            board[i][j] = "Y"
            if i > 0 && board[i - 1][j] == "O" {
                dfs(&board, i - 1, j)
            }

            if j < board[i].count - 1 && board[i][j + 1] == "O" {
                dfs(&board, i, j + 1)
            }

            if i < board.count - 1 && board[i + 1][j] == "O" {
                dfs(&board, i + 1, j)
            }

            if j > 0 && board[i][j - 1] == "O" {
                dfs(&board, i, j - 1)
            }
        }
    }
}

---

60ms

class Solution {
    func solve(_ board: inout [[Character]]) {
        guard board.count > 0 && board[0].count > 0 else {
            return
        }
        
        let countRow = board.count - 1
        let countCol = board[0].count - 1
        
        var visited = [[Bool]](repeating:[Bool](repeating: false, count: countCol+1), count: countRow+1)
        var boarder0Indexs = [(Int,Int)]()
        
        let direction  = [(-1,0),(1,0),(0,-1),(0,1)] // top bot left right
        
        for row in 0...countRow {
            for col in 0...countCol {
                if row == 0 || col == 0 || row == countRow || col == countCol {
                    if board[row][col] == "O" {
                        board[row][col] = "B"
                        boarder0Indexs.append((row,col))
                    }                    
                }
            }
        }
        
        for item in boarder0Indexs {
            let row = item.0
            let col = item.1
             
            var tempQueue = [(Int,Int)]()
            tempQueue.append(item)
            
            //bfs
            while (!tempQueue.isEmpty) {
                let count = tempQueue.count
                for _ in 0..<count {
                    let curItem = tempQueue.removeFirst()
                    let curRow = curItem.0
                    let curCol = curItem.1
                    //check adjacent cells 
                    for dirt in direction {
                        let nextLevelRow = curRow + dirt.0
                        let nextLevelCol = curCol + dirt.1  
                        //make sure not out of bounce
                        if nextLevelRow <= countRow && nextLevelRow >= 0 && nextLevelCol <= countCol && nextLevelCol >= 0 {
                            if !visited[nextLevelRow][nextLevelCol] {
                                if board[nextLevelRow][nextLevelCol] == "O" {
                                    board[nextLevelRow][nextLevelCol] = "B"
                                    tempQueue.append((nextLevelRow,nextLevelCol))
                                } 
                                visited[nextLevelRow][nextLevelCol] = true
                            }   
                        }                       
                    }
                }
            }       
        }
        for i in 0...countRow {
            for j in 0...countCol {
                if  board[i][j] == "B" {
                    board[i][j] = "O"
                } else if board[i][j] == "O" {
                    board[i][j] = "X"
                }
            }
        }
    }
}

---

80ms

class Solution {
    func solve(_ board: inout [[Character]]) {
        for i in 0..<board.count{
            for j in 0..<board[0].count{
                if (i==0 || i == board.count - 1 || j == 0 || j == board[0].count - 1) && board[i][j] == "O" {
                    board[i][j] = "M"
                    connected(i, j, &board)
                }
            }
        }
        for i in 0..<board.count{
            for j in 0..<board[0].count{
                if board[i][j] == "O" {
                    board[i][j] = "X"
                }
                else if board[i][j] == "M" {
                    board[i][j] = "O"
                }    
            }
        }
    }
    private func connected(_ i : Int, _ j : Int, _ board: inout [[Character]]){
        if i-1 > 0 && board[i-1][j] == "O" {
            board[i-1][j] = "M"
            connected(i-1, j, &board)
        }
        if i+1 < board.count-1 && board[i+1][j] == "O" {
            board[i+1][j] = "M"
            connected(i+1, j, &board)
        }
        if j-1 > 0 && board[i][j-1] == "O" {
            board[i][j-1] = "M"
            connected(i, j-1, &board)
        }
        if j+1 < board[i].count-1 && board[i][j+1] == "O" {
            board[i][j+1] = "M"
            connected(i, j+1, &board)
        }
    }
}

---

176ms

let X = Character("X")
let O = Character("O")

class Solution {

    func solve(_ board: inout [[Character]]) {
        guard let columnCount = board.first?.count else {
            return
        }
        let rowCount = board.count
        let uf = UnionFind(rowCount: rowCount, columnCount: columnCount)

        board.enumerated().forEach { i, row in
            row.enumerated().forEach { j, item in
                guard item == O else {
                    return
                }

                if i == 0 || i == rowCount - 1 || j == 0 || j == columnCount - 1 {
                    uf.open(i, j)
                }

                // top
                if i > 0 && board[i - 1][j] == O {
                    uf.union(i, j, i - 1, j)
                }

                // bottom
                if i < rowCount - 1 && board[i + 1][j] == O {
                    uf.union(i, j, i + 1, j)
                }

                // left
                if j > 0 && board[i][j - 1] == O {
                    uf.union(i, j, i, j - 1)
                }

                // right
                if j < columnCount - 1 && board[i][j + 1] == O {
                    uf.union(i, j, i, j + 1)
                }
            }
        }

        for i in 0..<rowCount {
            for j in 0..<columnCount where board[i][j] == O {
                if !uf.isOpen(i, j) {
                    board[i][j] = X
                }
            }
        }
    }

}

class UnionFind {

    var parent: [Int]
    var sizes: [Int]

    private let rowCount: Int
    private let columnCount: Int

    private var opened: [Bool]

    init(rowCount: Int, columnCount: Int) {
        self.rowCount = rowCount
        self.columnCount = columnCount

        let count = rowCount * columnCount

        sizes = Array(repeating: 1, count: count)
        parent = Array(repeating: 0, count: count)
        opened = Array(repeating: false, count: count)

        for i in 0..<count {
            parent[i] = i
        }
    }

    func isOpen(_ i: Int, _ j: Int) -> Bool {
        return opened[find(i, j)]
    }

    func open(_ i: Int, _ j: Int) {
        let index = calculateIndex(i, j)
        opened[index] = true
    }

    func union(_ li: Int, _ lj: Int, _ ri: Int, _ rj: Int) {
        let rootLeft = find(li, lj)
        let rootRight = find(ri, rj)

        if li == 0 || li == rowCount - 1 || lj == 0 || lj == columnCount - 1 {
            open(li, lj)
        }
        if ri == 0 || ri == rowCount - 1 || rj == 0 || rj == columnCount - 1 {
            open(ri, rj)
        }

        if rootLeft == rootRight {
            return
        }

        if opened[rootLeft] {
            parent[rootRight] = parent[rootLeft]
            sizes[rootLeft] += sizes[rootRight]
            return
        }
        if opened[rootRight] {
            parent[rootLeft] = parent[rootRight]
            sizes[rootRight] += sizes[rootLeft]
            return
        }

        if sizes[rootLeft] > sizes[rootRight] {
            parent[rootRight] = parent[rootLeft]
            sizes[rootLeft] += sizes[rootRight]
        } else {
            parent[rootLeft] = parent[rootRight]
            sizes[rootRight] += sizes[rootLeft]
        }
    }

    func find(_ i: Int, _ j: Int) -> Int {
        var index = calculateIndex(i, j)
        while index != parent[index] {
            parent[index] = parent[parent[index]]
            index = parent[index]
        }
        return index
    }

    private func calculateIndex(_ i: Int, _ j: Int) -> Int {
        return i * columnCount + j
    }
}

---

316ms

class Solution {
    func solve(_ board: inout [[Character]]) {
        for i in 0..<board.count
        {
            for j in 0..<board[i].count
            {
                if (i == 0 || i == board.count - 1 || j == 0 || j == board[i].count - 1) && board[i][j] == "O"
                {
                    solveDFS(&board, i, j)
                }
            }
        }
        for i in 0..<board.count
        {
            for j in 0..<board[i].count
            {
                if board[i][j] == "O" {board[i][j] = "X"}
                if board[i][j] == "$" {board[i][j] = "O"}
            }
        }
    }
    
    func solveDFS(_ board: inout [[Character]],_ i:Int,_ j:Int)
    {
        if board[i][j] == "O"
        {
            board[i][j] = "$"
            if i > 0 && board[i - 1][j] == "O"
            {
                solveDFS(&board, i - 1, j)
            }
            if j < board[i].count - 1 && board[i][j + 1] == "O"
            {
                solveDFS(&board, i, j + 1)
            }
            if i < board.count - 1 && board[i + 1][j] == "O"
            {
                solveDFS(&board, i + 1, j)
            }
            if j > 1 && board[i][j - 1] == "O"
            {
                solveDFS(&board, i, j - 1)
            }
        }
    }
}