Update Solution.py

Author: yanglbme

solution/2000-2099/2096.Step-By-Step Directions From a Binary Tree Node to Another/Solution.py

@@ -4,40 +4,41 @@
 #         self.val = val
 #         self.left = left
 #         self.right = right
+
+
 class Solution:
     def getDirections(
         self, root: Optional[TreeNode], startValue: int, destValue: int
     ) -> str:
-        edges = defaultdict(list)
-        ans = None
-        visited = set()
+        def lca(node: Optional[TreeNode], p: int, q: int):
+            if node is None or node.val in (p, q):
+                return node
+            left = lca(node.left, p, q)
+            right = lca(node.right, p, q)
+            if left and right:
+                return node
+            return left or right
+
+        def dfs(node: Optional[TreeNode], x: int, path: List[str]):
+            if node is None:
+                return False
+            if node.val == x:
+                return True
+            path.append("L")
+            if dfs(node.left, x, path):
+                return True
+            path[-1] = "R"
+            if dfs(node.right, x, path):
+                return True
+            path.pop()
+            return False
+
+        node = lca(root, startValue, destValue)
 
-        def traverse(root):
-            if not root:
-                return
-            if root.left:
-                edges[root.val].append([root.left.val, 'L'])
-                edges[root.left.val].append([root.val, 'U'])
-            if root.right:
-                edges[root.val].append([root.right.val, 'R'])
-                edges[root.right.val].append([root.val, 'U'])
-            traverse(root.left)
-            traverse(root.right)
+        path_to_start = []
+        path_to_dest = []
 
-        def dfs(start, dest, t):
-            nonlocal ans
-            if start in visited:
-                return
-            if start == dest:
-                if ans is None or len(ans) > len(t):
-                    ans = ''.join(t)
-                return
-            visited.add(start)
-            for d, k in edges[start]:
-                t.append(k)
-                dfs(d, dest, t)
-                t.pop()
+        dfs(node, startValue, path_to_start)
+        dfs(node, destValue, path_to_dest)
 
-        traverse(root)
-        dfs(startValue, destValue, [])
-        return ans
+        return "U" * len(path_to_start) + "".join(path_to_dest)