79. Word Search

swift/79-Word-Search.swift

@@ -0,0 +1,94 @@
+class Solution {
+    let dirX: [Int] = [-1, 1, 0, 0]
+    let dirY: [Int] = [0, 0, -1, 1]
+
+    func exist(_ board: [[Character]], _ word: String) -> Bool {
+        let ROWS = board.count
+        let COLS = board[0].count
+
+        var visited = [[Bool]](
+            repeating: [Bool](repeating: false, count: COLS),
+            count: ROWS
+        )
+
+        var wordArr: [Character] = Array(word)
+
+        for r in 0..<ROWS {
+            for c in 0..<COLS {
+                visited[r][c] = true
+
+                if dfs(
+                    startRow: r, 
+                    startCol: c, 
+                    &visited, 
+                    board, 
+                    &wordArr,
+                    startIdx: 0
+                ) == true {
+                    return true
+                }
+
+                visited[r][c] = false
+            }
+        }
+
+        return false
+    }
+}
+
+private extension Solution {
+    func isWithinBounds(row: Int, col: Int, _ board: [[Character]]) -> Bool {
+        ((row >= 0) && (col >= 0) &&
+        (row < board.count) && (col < board[0].count))
+    }
+
+
+    func dfs(
+        startRow row: Int, 
+        startCol col: Int, 
+        _ visited: inout [[Bool]],
+        _ board: [[Character]],
+        _ wordArr: inout [Character],
+        startIdx index: Int
+    ) -> Bool {
+        let strLen = wordArr.count
+
+        // Last index check
+        if index == (strLen - 1) {
+            return board[row][col] == wordArr[index]
+        }
+
+        // Edge case
+        guard index < strLen else { return false }
+        guard board[row][col] == wordArr[index] else { return false }
+
+        for (dX, dY) in zip(dirX, dirY) {
+            let rowNew = row + dX
+            let colNew = col + dY
+
+            guard isWithinBounds(row: rowNew, col: colNew, board) else { continue }
+            guard visited[rowNew][colNew] == false else { continue }
+
+            // Visit
+            visited[rowNew][colNew] = true
+
+            // Recursive DFS
+            if dfs(
+                startRow: rowNew, 
+                startCol: colNew, 
+                &visited, 
+                board, 
+                &wordArr, 
+                startIdx: index + 1
+            ) == true {
+                return true
+            }
+
+            // Unvisit [for backtrack]
+            visited[rowNew][colNew] = false
+        }
+
+        return false
+    }
+}
+