feat: Add solution for LeetCode problem 79

Author: WhiteHyun

word-search/WhiteHyun.swift

@@ -0,0 +1,49 @@
+//  
+//  79. Word Search
+//  https://leetcode.com/problems/word-search/description/
+//  Dale-Study
+//  
+//  Created by WhiteHyun on 2024/06/28.
+//  
+
+class Solution {
+  func exist(_ board: [[Character]], _ word: String) -> Bool {
+    let rows = board.count
+    let cols = board[0].count
+    let word = Array(word)
+    var visited = Array(repeating: Array(repeating: false, count: cols), count: rows)
+
+    for row in 0 ..< rows {
+      for col in 0 ..< cols {
+        if board[row][col] == word[0], dfs(board, word, row, col, 0, &visited) {
+          return true
+        }
+      }
+    }
+
+    return false
+  }
+
+  private func dfs(_ board: [[Character]], _ word: [Character], _ row: Int, _ col: Int, _ index: Int, _ visited: inout [[Bool]]) -> Bool {
+    if index == word.count {
+      return true
+    }
+
+    if row < 0 || row >= board.count || col < 0 || col >= board[0].count || visited[row][col] || board[row][col] != word[index] {
+      return false
+    }
+
+    visited[row][col] = true
+
+    let directions = [(0, 1), (1, 0), (0, -1), (-1, 0)]
+
+    for (dx, dy) in directions {
+      if dfs(board, word, row + dx, col + dy, index + 1, &visited) {
+        return true
+      }
+    }
+
+    visited[row][col] = false
+    return false
+  }
+}