Merge pull request #927 from firepunch/week7

[Mirim] Week7

mirim/2024-03-17-buildTree-105.py

@@ -0,0 +1,17 @@
+# https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/description/
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+
+
+class Solution:
+    def buildTree(self, preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
+        if inorder:
+            index = inorder.index(preorder.pop(0))
+            root = TreeNode(inorder[index])
+            root.left = self.buildTree(preorder, inorder[:index])
+            root.right = self.buildTree(preorder, inorder[index + 1 :])
+            return root

mirim/2024-03-17-buildTree-106.py

@@ -0,0 +1,18 @@
+# https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+
+
+class Solution:
+    def buildTree(self, inorder: List[int], postorder: List[int]) -> Optional[TreeNode]:
+        if not inorder or not postorder:
+            return None
+        root = TreeNode(postorder[-1])
+        index = inorder.index(postorder[-1])
+        root.left = self.buildTree(inorder[:index], postorder[:index])
+        root.right = self.buildTree(inorder[index + 1 :], postorder[index:-1])
+        return root

mirim/2024-03-17-distanceK.py

@@ -0,0 +1,44 @@
+# https://leetcode.com/problems/all-nodes-distance-k-in-binary-tree/description/
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+
+class Solution:
+    def distanceK(self, root: TreeNode, target: TreeNode, k: int) -> List[int]:
+        res = []
+        if k == 0:
+            res = [target.val]
+            return res
+
+        graph = collections.defaultdict(list)
+        q = collections.deque([root])
+        while q:
+            node = q.popleft()
+            if node.left:
+                graph[node].append(node.left)
+                graph[node.left].append(node)
+                q.append(node.left)
+            if node.right:
+                graph[node].append(node.right)
+                graph[node.right].append(node)
+                q.append(node.right)
+
+        visited = set([target])
+        q = collections.deque([target])
+        level = 0
+        while q:
+            for i in range(len(q)):
+                node = q.popleft()
+                if level == k:
+                    res.append(node.val)
+                else:
+                    for edge in graph[node]:
+                        if edge not in visited:
+                            visited.add(edge)
+                            q.append(edge)
+            level += 1
+        return res