0200-number-of-islands

0200-number-of-islands.playground/Contents.swift

@@ -0,0 +1,62 @@
+/// 200. Number of Islands
+/// 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.
+
+import XCTest
+
+/// Approach: BFS
+func numIslands(_ grid: [[Character]]) -> Int {
+    var grid = grid
+    let m = grid.count
+    guard m > 0 else { return 0}
+    let n = grid[0].count
+    var count = 0
+    for i in 0..<m {
+        for j in 0..<n {
+            guard grid[i][j] == "1" else { continue }
+            count += 1
+            var queue: [Int] = []
+            queue.append(i * n + j)
+            grid[i][j] = "v"
+            var head = 0
+            while head < queue.count {
+                let index = queue[head]
+                head += 1
+                let r = index / n
+                let c = index % n
+                if r > 0, grid[r - 1][c] == "1" {
+                    queue.append((r - 1) * n + c)
+                    grid[r - 1][c] = "v"
+                }
+                if c > 0, grid[r][c - 1] == "1" {
+                    queue.append(r * n + c - 1)
+                    grid[r][c - 1] = "v"
+                }
+                if r + 1 < m, grid[r + 1][c] == "1" {
+                    queue.append((r + 1) * n + c)
+                    grid[r + 1][c] = "v"
+                }
+                if c + 1 < n, grid[r][c + 1] == "1" {
+                    queue.append(r * n + c + 1)
+                    grid[r][c + 1] = "v"
+                }
+            }
+        }
+    }
+    return count
+}
+
+class Tests: XCTestCase {
+    func testExample() {
+        let grid: [[Character]] = [
+            ["1", "1", "1", "1", "0"],
+            ["1", "1", "0", "1", "0"],
+            ["1", "1", "0", "0", "0"],
+            ["1", "0", "0", "0", "0"],
+        ]
+        XCTAssertEqual(numIslands(grid), 1)
+    }
+}
+
+Tests.defaultTestSuite.run()

0200-number-of-islands.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos' executeOnSourceChanges='false'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

README.md

@@ -54,6 +54,7 @@ You can visit the pages below to search problems by company tags. Then come back
 33 | [Search in Rotated Sorted Array](https://leetcode.com/problems/search-in-rotated-sorted-array/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0033-search-in-rotated-sorted-array.playground/Contents.swift) | Binary Search
 66 | [Plus One](https://leetcode.com/problems/plus-one/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0066-plus-one.playground/Contents.swift) | Math
 84 | [Largest Rectangle in Histogram](https://leetcode.com/problems/largest-rectangle-in-histogram/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0084-largest-rectangle-in-histogram.playground/Contents.swift) | Stack
+200 | [Number of Islands](https://leetcode.com/problems/number-of-islands/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0200-number-of-islands.playground/Contents.swift) | BFS
 482 | [License Key Formatting](https://leetcode.com/problems/license-key-formatting/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0482-license-key-formatting.playground/Contents.swift) | String
 681 | [Next Closest Time](https://leetcode.com/problems/next-closest-time/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0681-next-closest-time.playground/Contents.swift) | Simulation
 683 | [K Empty Slots](https://leetcode.com/problems/k-empty-slots/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0683-k-empty-slots.playground/Contents.swift) | Sliding Window