Update 079._word_search.md

Author: 0xkookoo

docs/Leetcode_Solutions/Python/079._word_search.md

@@ -54,21 +54,20 @@ class Solution:
         """
         if not board:
             return False
+        if not word:
+            return True
 
         row = len(board)
         col = len(board[0]) if row else 0
 
-        if not word or word == '':
-            return True
-        
         def dfs(i, j, idx):
-            if i < 0 or j < 0 or i > row-1 or j > col-1 or board[i][j] != word[idx]:
+            if not 0 <= i <= row - 1 or not 0 <= j <= col - 1 or board[i][j] != word[idx]:
                 return False
             if idx == len(word) - 1:
                 return True
-            board[i][j] = '*'  # mark as visited
+            board[i][j] = '*'
             res = dfs(i+1, j, idx+1) or dfs(i, j+1, idx+1) or dfs(i-1, j, idx+1) or dfs(i, j-1, idx+1)
-            board[i][j] = word[idx] # backtrack
+            board[i][j] = word[idx]
             return res
 
         return any(dfs(i, j, 0) for i in range(row) for j in range(col))