word-search solution

Author: sun912

word-search/sun912.py

@@ -0,0 +1,41 @@
+"""
+TC: O(ROWS*COLS*4^word length)
+SC: O(ROWS*COLS*word length)
+"""
+
+class Solution:
+    def exist(self, board: List[List[str]], word: str) -> bool:
+        ROWS = len(board)
+        COLS = len(board[0])
+        path = set()
+
+        def dfs(r,c,i):
+            if i == len(word):
+                return True
+
+            if (r < 0 or
+                    c < 0 or
+                    r >= ROWS or
+                    c >= COLS or
+                    word[i] != board[r][c] or
+                    (r,c) in path
+            ):
+                return False
+
+            path.add((r,c))
+
+            res = (dfs(r+1, c, i+1) or
+                   dfs(r, c+1, i+1) or
+                   dfs(r-1, c, i+1) or
+                   dfs(r, c-1, i+1)
+                   )
+            path.remove((r,c))
+            return res
+
+        for r in range(ROWS):
+            for c in range(COLS):
+                if dfs(r,c, 0): return True
+
+        return False
+
+