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0079-word-search/0079-word-search.py

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+class Solution:
+    def exist(self, board: List[List[str]], word: str) -> bool:
+        def existFromStart(x: int, y: int, wordLeft: str, used: Set[Tuple[int, int]]):
+            if len(wordLeft) == 0:
+                return True
+
+            if board[x][y] != wordLeft[0]:
+                return False
+
+            if len(wordLeft) == 1:
+                return True
+
+            newUsed = used.union(set([(x, y)]))
+
+            if x + 1 < len(board) and (x+1,y) not in used and existFromStart(x + 1, y, wordLeft[1:], newUsed):
+                return True
+            
+            if x - 1 >= 0 and (x-1,y) not in used and existFromStart(x - 1, y, wordLeft[1:], newUsed):
+                return True
+
+            if y + 1 < len(board[x]) and (x,y+1) not in used and existFromStart(x, y + 1, wordLeft[1:], newUsed):
+                return True
+            
+            if y - 1 >= 0 and (x,y-1) not in used and existFromStart(x, y - 1, wordLeft[1:], newUsed):
+                return True
+
+            return False
+
+        for i in range(len(board)):
+            for j in range(len(board[i])):
+                if existFromStart(i, j, word, set({})):
+                    return True
+
+        return False
+