Adding 200. Number of Islands in Swift

Author: Mahim1997

swift/200-Number-of-Islands.swift

@@ -0,0 +1,58 @@
+class Solution {
+    
+    func numIslands(_ grid: [[Character]]) -> Int {
+        let ROWS = grid.count
+        let COLS = grid[0].count
+        
+        var visited = [[Bool]](
+            repeating: [Bool](repeating: false, count: COLS),
+            count: ROWS
+        )
+        var count: Int = 0
+        
+        // Helper function to check if is within
+        func isWithin(row: Int, col: Int) -> Bool {
+            return (
+                (row >= 0) && (col >= 0) &&
+                (row < ROWS) && (col < COLS)
+            )
+        }
+        
+        // Helper function to check if cell is land or not
+        func isLand(row: Int, col: Int) -> Bool {
+            return grid[row][col] == "1"
+        }
+        
+        let movementsX = [-1, 1, 0,  0]
+        let movementsY = [0,  0, -1, 1]
+        
+        // Helper DFS function to 'visit' the grid
+        func dfs(row: Int, col: Int) {
+            // visit each child
+            for (dirX, dirY) in zip(movementsX, movementsY) {
+                let rowNew = row + dirX
+                let colNew = col + dirY
+                
+                guard isWithin(row: rowNew, col: colNew) else { continue }
+                guard visited[rowNew][colNew] == false else { continue }
+                guard isLand(row: rowNew, col: colNew) else { continue }
+                
+                visited[rowNew][colNew] = true
+                dfs(row: rowNew, col: colNew)
+            }
+        }
+        
+        for r in 0..<ROWS {
+            for c in 0..<COLS {
+                guard visited[r][c] == false  else { continue }
+                guard isLand(row: r, col: c)  else { continue }
+                
+                visited[r][c] = true
+                dfs(row: r, col: c)
+                count += 1
+            }
+        }
+        
+        return count
+    }
+}