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'

 給定一個二維的矩陣，包含 'X' 和 'O'（字母 O）。

找到所有被 'X' 圍繞的區域，並將這些區域裡所有的 'O' 用 'X' 填充。

示例:

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

執行你的函式後，矩陣變為：

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

解釋:

被圍繞的區間不會存在於邊界上，換句話說，任何邊界上的 'O' 都不會被填充為 'X'。 任何不在邊界上，或不與邊界上的 'O' 相連的 'O' 最終都會被填充為 'X'。如果兩個元素在水平或垂直方向相鄰，則稱它們是“相連”的。

52ms

 1 class Solution {
 2     func solve(_ board: inout [[Character]]) {
 3         let h = board.count
 4         guard h > 2 else { return }
 5         
 6         let w = board[0].count
 7         guard w > 2 else { return }
 8         
 9         for i in 0..<h {
10             mark(&board, i, 0)
11             mark(&board, i, w - 1)
12         }
13         
14         for j in 0..<w {
15             mark(&board, 0, j)
16             mark(&board, h - 1, j)
17         }
18         
19         for i in 0..<h {
20             for j in 0..<w {
21                 if board[i][j] == "O" {
22                    board[i][j] = "X"
23                 } else if board[i][j] == "T" {
24                    board[i][j] = "O"
25                 }
26             }
27         }
28     }
29     
30     func mark(_ board: inout [[Character]], _ i: Int, _ j: Int) {
31         guard i >= 0 && i < board.count else { return }
32         guard j >= 0 && j < board[i].count else { return }
33         guard board[i][j] == "O" else { return }
34         
35         board[i][j] = "T"
36         
37         mark(&board, i - 1, j)
38         mark(&board, i + 1, j)
39         mark(&board, i, j - 1)
40         mark(&board, i, j + 1)
41     }
42 }

56ms

 1 class Solution {
 2     func solve(_ board: inout [[Character]]) {
 3         for i in 0..<board.count {
 4             for j in 0..<board[i].count {
 5                 if (i == 0 || i == board.count - 1 || j == 0 || j == board[i].count - 1) && board[i][j] == "O" {
 6                     dfs(&board, i, j)
 7                 }
 8 
 9             }
10         }
11         for i in 0..<board.count {
12             for j in 0..<board[i].count {
13                 if board[i][j] == "O" {
14                     board[i][j] = "X"
15                 }
16                 if board[i][j] == "Y" {
17                     board[i][j] = "O"
18                 }
19             }
20         }
21     }
22     private func dfs(_ board: inout [[Character]], _ i: Int, _ j: Int) {
23         if board[i][j] == "O" {
24 
25             board[i][j] = "Y"
26             if i > 0 && board[i - 1][j] == "O" {
27                 dfs(&board, i - 1, j)
28             }
29 
30             if j < board[i].count - 1 && board[i][j + 1] == "O" {
31                 dfs(&board, i, j + 1)
32             }
33 
34             if i < board.count - 1 && board[i + 1][j] == "O" {
35                 dfs(&board, i + 1, j)
36             }
37 
38             if j > 0 && board[i][j - 1] == "O" {
39                 dfs(&board, i, j - 1)
40             }
41         }
42     }
43 }

60ms

 1 class Solution {
 2     func solve(_ board: inout [[Character]]) {
 3         guard board.count > 0 && board[0].count > 0 else {
 4             return
 5         }
 6         
 7         let countRow = board.count - 1
 8         let countCol = board[0].count - 1
 9         
10         var visited = [[Bool]](repeating:[Bool](repeating: false, count: countCol+1), count: countRow+1)
11         var boarder0Indexs = [(Int,Int)]()
12         
13         let direction  = [(-1,0),(1,0),(0,-1),(0,1)] // top bot left right
14         
15         for row in 0...countRow {
16             for col in 0...countCol {
17                 if row == 0 || col == 0 || row == countRow || col == countCol {
18                     if board[row][col] == "O" {
19                         board[row][col] = "B"
20                         boarder0Indexs.append((row,col))
21                     }                    
22                 }
23             }
24         }
25         
26         for item in boarder0Indexs {
27             let row = item.0
28             let col = item.1
29              
30             var tempQueue = [(Int,Int)]()
31             tempQueue.append(item)
32             
33             //bfs
34             while (!tempQueue.isEmpty) {
35                 let count = tempQueue.count
36                 for _ in 0..<count {
37                     let curItem = tempQueue.removeFirst()
38                     let curRow = curItem.0
39                     let curCol = curItem.1
40                     //check adjacent cells 
41                     for dirt in direction {
42                         let nextLevelRow = curRow + dirt.0
43                         let nextLevelCol = curCol + dirt.1  
44                         //make sure not out of bounce
45                         if nextLevelRow <= countRow && nextLevelRow >= 0 && nextLevelCol <= countCol && nextLevelCol >= 0 {
46                             if !visited[nextLevelRow][nextLevelCol] {
47                                 if board[nextLevelRow][nextLevelCol] == "O" {
48                                     board[nextLevelRow][nextLevelCol] = "B"
49                                     tempQueue.append((nextLevelRow,nextLevelCol))
50                                 } 
51                                 visited[nextLevelRow][nextLevelCol] = true
52                             }   
53                         }                       
54                     }
55                 }
56             }       
57         }
58         for i in 0...countRow {
59             for j in 0...countCol {
60                 if  board[i][j] == "B" {
61                     board[i][j] = "O"
62                 } else if board[i][j] == "O" {
63                     board[i][j] = "X"
64                 }
65             }
66         }
67     }
68 }

80ms

 1 class Solution {
 2     func solve(_ board: inout [[Character]]) {
 3         for i in 0..<board.count{
 4             for j in 0..<board[0].count{
 5                 if (i==0 || i == board.count - 1 || j == 0 || j == board[0].count - 1) && board[i][j] == "O" {
 6                     board[i][j] = "M"
 7                     connected(i, j, &board)
 8                 }
 9             }
10         }
11         for i in 0..<board.count{
12             for j in 0..<board[0].count{
13                 if board[i][j] == "O" {
14                     board[i][j] = "X"
15                 }
16                 else if board[i][j] == "M" {
17                     board[i][j] = "O"
18                 }    
19             }
20         }
21     }
22     private func connected(_ i : Int, _ j : Int, _ board: inout [[Character]]){
23         if i-1 > 0 && board[i-1][j] == "O" {
24             board[i-1][j] = "M"
25             connected(i-1, j, &board)
26         }
27         if i+1 < board.count-1 && board[i+1][j] == "O" {
28             board[i+1][j] = "M"
29             connected(i+1, j, &board)
30         }
31         if j-1 > 0 && board[i][j-1] == "O" {
32             board[i][j-1] = "M"
33             connected(i, j-1, &board)
34         }
35         if j+1 < board[i].count-1 && board[i][j+1] == "O" {
36             board[i][j+1] = "M"
37             connected(i, j+1, &board)
38         }
39     }
40 }

176ms

  1 let X = Character("X")
  2 let O = Character("O")
  3 
  4 class Solution {
  5 
  6     func solve(_ board: inout [[Character]]) {
  7         guard let columnCount = board.first?.count else {
  8             return
  9         }
 10         let rowCount = board.count
 11         let uf = UnionFind(rowCount: rowCount, columnCount: columnCount)
 12 
 13         board.enumerated().forEach { i, row in
 14             row.enumerated().forEach { j, item in
 15                 guard item == O else {
 16                     return
 17                 }
 18 
 19                 if i == 0 || i == rowCount - 1 || j == 0 || j == columnCount - 1 {
 20                     uf.open(i, j)
 21                 }
 22 
 23                 // top
 24                 if i > 0 && board[i - 1][j] == O {
 25                     uf.union(i, j, i - 1, j)
 26                 }
 27 
 28                 // bottom
 29                 if i < rowCount - 1 && board[i + 1][j] == O {
 30                     uf.union(i, j, i + 1, j)
 31                 }
 32 
 33                 // left
 34                 if j > 0 && board[i][j - 1] == O {
 35                     uf.union(i, j, i, j - 1)
 36                 }
 37 
 38                 // right
 39                 if j < columnCount - 1 && board[i][j + 1] == O {
 40                     uf.union(i, j, i, j + 1)
 41                 }
 42             }
 43         }
 44 
 45         for i in 0..<rowCount {
 46             for j in 0..<columnCount where board[i][j] == O {
 47                 if !uf.isOpen(i, j) {
 48                     board[i][j] = X
 49                 }
 50             }
 51         }
 52     }
 53 
 54 }
 55 
 56 class UnionFind {
 57 
 58     var parent: [Int]
 59     var sizes: [Int]
 60 
 61     private let rowCount: Int
 62     private let columnCount: Int
 63 
 64     private var opened: [Bool]
 65 
 66     init(rowCount: Int, columnCount: Int) {
 67         self.rowCount = rowCount
 68         self.columnCount = columnCount
 69 
 70         let count = rowCount * columnCount
 71 
 72         sizes = Array(repeating: 1, count: count)
 73         parent = Array(repeating: 0, count: count)
 74         opened = Array(repeating: false, count: count)
 75 
 76         for i in 0..<count {
 77             parent[i] = i
 78         }
 79     }
 80 
 81     func isOpen(_ i: Int, _ j: Int) -> Bool {
 82         return opened[find(i, j)]
 83     }
 84 
 85     func open(_ i: Int, _ j: Int) {
 86         let index = calculateIndex(i, j)
 87         opened[index] = true
 88     }
 89 
 90     func union(_ li: Int, _ lj: Int, _ ri: Int, _ rj: Int) {
 91         let rootLeft = find(li, lj)
 92         let rootRight = find(ri, rj)
 93 
 94         if li == 0 || li == rowCount - 1 || lj == 0 || lj == columnCount - 1 {
 95             open(li, lj)
 96         }
 97         if ri == 0 || ri == rowCount - 1 || rj == 0 || rj == columnCount - 1 {
 98             open(ri, rj)
 99         }
100 
101         if rootLeft == rootRight {
102             return
103         }
104 
105         if opened[rootLeft] {
106             parent[rootRight] = parent[rootLeft]
107             sizes[rootLeft] += sizes[rootRight]
108             return
109         }
110         if opened[rootRight] {
111             parent[rootLeft] = parent[rootRight]
112             sizes[rootRight] += sizes[rootLeft]
113             return
114         }
115 
116         if sizes[rootLeft] > sizes[rootRight] {
117             parent[rootRight] = parent[rootLeft]
118             sizes[rootLeft] += sizes[rootRight]
119         } else {
120             parent[rootLeft] = parent[rootRight]
121             sizes[rootRight] += sizes[rootLeft]
122         }
123     }
124 
125     func find(_ i: Int, _ j: Int) -> Int {
126         var index = calculateIndex(i, j)
127         while index != parent[index] {
128             parent[index] = parent[parent[index]]
129             index = parent[index]
130         }
131         return index
132     }
133 
134     private func calculateIndex(_ i: Int, _ j: Int) -> Int {
135         return i * columnCount + j
136     }
137 }

316ms

 1 class Solution {
 2     func solve(_ board: inout [[Character]]) {
 3         for i in 0..<board.count
 4         {
 5             for j in 0..<board[i].count
 6             {
 7                 if (i == 0 || i == board.count - 1 || j == 0 || j == board[i].count - 1) && board[i][j] == "O"
 8                 {
 9                     solveDFS(&board, i, j)
10                 }
11             }
12         }
13         for i in 0..<board.count
14         {
15             for j in 0..<board[i].count
16             {
17                 if board[i][j] == "O" {board[i][j] = "X"}
18                 if board[i][j] == "$" {board[i][j] = "O"}
19             }
20         }
21     }
22     
23     func solveDFS(_ board: inout [[Character]],_ i:Int,_ j:Int)
24     {
25         if board[i][j] == "O"
26         {
27             board[i][j] = "$"
28             if i > 0 && board[i - 1][j] == "O"
29             {
30                 solveDFS(&board, i - 1, j)
31             }
32             if j < board[i].count - 1 && board[i][j + 1] == "O"
33             {
34                 solveDFS(&board, i, j + 1)
35             }
36             if i < board.count - 1 && board[i + 1][j] == "O"
37             {
38                 solveDFS(&board, i + 1, j)
39             }
40             if j > 1 && board[i][j - 1] == "O"
41             {
42                 solveDFS(&board, i, j - 1)
43             }
44         }
45     }
46 }