[Swift]LeetCode200.島嶼的個數 | Number of Islands

時間 2019-11-11

標籤 swift leetcode200 leetcode 島嶼個數 number islands 欄目 Swift 简体版

原文原文鏈接

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Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.git

Example 1:github

Input:
11110
11010
11000
00000

Output: 1

Example 2:微信

Input:
11000
11000
00100
00011

Output: 3

Example 1:spa

Input:
11110
11010
11000
00000

Output: 1

Example 2:code

Input:
11000
11000
00100
00011

Output: 3

給定一個由 '1'（陸地）和 '0'（水）組成的的二維網格，計算島嶼的數量。一個島被水包圍，而且它是經過水平方向或垂直方向上相鄰的陸地鏈接而成的。你能夠假設網格的四個邊均被水包圍。orm

示例 1:htm

示例 2:blog

260ms

 1 class Solution {
 2     func numIslands(_ grid: [[Character]]) -> Int {
 3         var map = grid
 4         let row = map.count
 5         if row == 0 {return 0}
 6         let col = map[0].count
 7         var count = 0
 8         for i in 0..<row {
 9             for j in 0..<col {
10                 if map[i][j] == "1" {
11                     dfs(&map, i, j, row, col)
12                     count += 1
13                 }
14             }
15         }        
16         return count
17     }
18     func dfs(_ map: inout [[Character]], _ i: Int, _ j: Int, _ row: Int, _ col: Int) {
19         if (i >= 0 && i < row && j >= 0 && j < col && map[i][j] == "1") {
20             map[i][j] = "2"
21             dfs(&map, i, j-1, row, col);
22             dfs(&map, i-1, j, row, col);
23             dfs(&map, i, j+1, row, col);
24             dfs(&map, i+1, j, row, col);
25         }
26     }
27 }

268ms

 1 class Solution {
 2     func numIslands(_ grid: [[Character]]) -> Int {
 3         var map = grid
 4         let row = map.count
 5         if row == 0 {return 0}
 6         let col = map[0].count
 7         var count = 0
 8         for i in 0..<row {
 9             for j in 0..<col {
10                 if map[i][j] == "1" {
11                     dfs(&map, i, j, row, col)
12                     count += 1
13                 }
14             }
15         }        
16         return count
17     }
18     func dfs(_ map: inout [[Character]], _ i: Int, _ j: Int, _ row: Int, _ col: Int) {
19         if (i >= 0 && i < row && j >= 0 && j < col && map[i][j] == "1") {
20             map[i][j] = "2"
21             let index = [0,-1,0,1,0]
22             for k in 0..<(index.count - 1) {
23                 dfs(&map, i + index[k], j + index[k + 1], row, col)
24             }
25         }
26     }
27 }

288ms

 1 class Solution {
 2   func numIslands(_ grid: [[Character]]) -> Int {
 3         var grid = grid
 4         var count = 0
 5         
 6         for row in grid.indices {
 7             for col in 0..<grid[row].count where grid[row][col] == "1" { //find the first point of contact
 8                 
 9                 //dfs(grid: &grid, row: row, col: col)
10                 
11                 bfs(grid: &grid, row: row, col: col)
12                 
13                 count = count + 1 // found an island
14             }
15         }
16         
17         return count
18     }
19     
20     func bfs(grid: inout [[Character]], row: Int, col: Int) {
21         // bfs 只call了一次，因此能夠直接默認進來的是1
22         var queue = [(Int, Int)]()
23         queue.append((row, col))
24         grid[row][col] = "0"
25 
26         while !queue.isEmpty {
27             let pair = queue.removeFirst()  //don't use dropFirst
28             
29             let x = pair.0
30             let y = pair.1
31 
32             //up part
33             if x > 0, grid[x - 1][y] == "1" {
34                 grid[x - 1][y] = "0" // mark as visited
35                 queue.append((x - 1, y))
36             }
37 
38             //down part
39             if x < grid.count - 1, grid[x + 1][y] == "1" {
40                 grid[x + 1][y] = "0" // mark as visited
41                 queue.append((x + 1, y))
42             }
43 
44             //left part
45             if y > 0, grid[x][y - 1] == "1" {
46                 grid[x ][y - 1] = "0" // mark as visited
47                 queue.append((x, y - 1))
48             }
49 
50             //right part
51             if y < grid[x].count - 1, grid[x][y + 1] == "1" {
52                 grid[x ][y + 1] = "0" // mark as visited
53                 queue.append((x, y + 1))
54             }
55         }
56     }
57     
58     func dfs(grid: inout [[Character]], row: Int, col: Int) {
59         //dfs: pre order tree: me left righ => me, up, down, left right
60         
61         // me step
62         guard grid[row][col] == "1" else { return }
63         
64         grid[row][col] = "0"// mark as visited, smart
65         
66         //up part
67         if row > 0, grid[row - 1][col] == "1" {
68             dfs(grid: &grid, row: row - 1, col: col)
69         }
70         
71         //down part
72         if row < grid.count - 1, grid[row + 1][col] == "1" {
73             dfs(grid: &grid, row: row + 1, col: col)
74         }
75         
76         //left part
77         if col > 0, grid[row][col - 1] == "1" {
78             dfs(grid: &grid, row: row, col: col - 1)
79         }
80         
81         //right part
82         if col < grid[row].count - 1, grid[row][col + 1] == "1" {
83             dfs(grid: &grid, row: row, col: col + 1)
84         }
85         
86     }
87 }

292ms

 1 class Solution {
 2     func numIslands(_ grid: [[Character]]) -> Int {
 3         guard !grid.isEmpty, !grid[0].isEmpty else { return 0 }
 4         
 5         var queue = [[Int]]()
 6         var grid = grid
 7         var count = 0
 8         
 9         for i in 0..<grid.count {
10             for j in 0..<grid[0].count {
11                 if grid[i][j] == "1" {
12                     queue.append([i, j])
13                     count += 1
14                     markIsland(&grid, &queue)
15                 }
16             }
17         }
18         return count
19     }
20     
21     
22     private let dc = [-1, 1, 0, 0]
23     private let dr = [0, 0, 1, -1]
24     
25     private func markIsland(_ grid: inout [[Character]], _ queue: inout [[Int]]) {
26         while !queue.isEmpty {
27             let curr = queue.removeFirst()
28             for i in 0..<dc.count {
29                 let row = curr[0] + dr[i]
30                 let column = curr[1] + dc[i]
31                 if row < 0 || row >= grid.count || column < 0 || column >= grid[0].count || grid[row][column] == "0" {
32                     continue
33                 }
34                 grid[row][column] = "0"
35                 queue.append([row, column])
36             }
37         }
38     }
39 }

296ms

 1 class Solution {
 2     func numIslands(_ grid: [[Character]]) -> Int {
 3         guard grid.count > 0, grid[0].count > 0 else {
 4             return 0
 5         }
 6         var result = 0
 7         
 8         var dirs = [[0, 1], [1, 0], [0, -1], [-1, 0]]
 9         
10         var memo = [[Bool]](repeating:[Bool](repeating:false, count:grid[0].count), count:grid.count)
11         
12         func dfs(i:Int, j:Int) {
13             if i < 0 || j < 0 || i >= grid.count || j >= grid[0].count || memo[i][j] == true || grid[i][j] == "0" {
14                 return
15             }
16             
17             memo[i][j] = true
18             
19             for dir in dirs {
20                 dfs(i:i + dir[0], j: j + dir[1])
21             }
22         }
23         
24         for i in 0..<grid.count {
25             for j in 0..<grid[i].count {
26                 if memo[i][j] == true || grid[i][j] == "0" {
27                     continue
28                 } else {
29                     result += 1
30                     dfs(i:i, j:j)
31                 }
32             }
33         }
34         
35         return result
36     }
37 }

452ms

 1 class Solution {
 2     
 3     func numIslands(_ grid: [[Character]]) -> Int {
 4         
 5         var map = grid
 6         let n = map.count;
 7         if n == 0 { return 0 }
 8         let m = map[0].count
 9         var count = 0
10         
11          func emptMap(_ map: inout [[Character]], i: Int, j: Int) {
12             if (i < 0 || j<0 || i>=n || j>=m || map[i][j] != "1") { return }
13             map[i][j] = "0";
14             // 遞歸清除全部地點
15             emptMap(&map, i: i+1, j: j)
16             emptMap(&map, i: i-1, j: j)
17             emptMap(&map, i: i, j: j+1)
18             emptMap(&map, i: i, j: j-1)
19         }
20         
21         for (i,v) in map.enumerated() {
22             for (j,_) in v.enumerated () {
23                 if (map[i][j] == "1") {
24                     emptMap(&map, i: i, j: j)
25                     count = count + 1
26                 }
27             }
28         }
29         
30         return count
31     }
32 }

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