8.10笔记

105. 从前序与中序遍历序列构造二叉树（递归）

class Solution(object):
    def buildTree(self, preorder, inorder):
        """
        :type preorder: List[int]
        :type inorder: List[int]
        :rtype: TreeNode
        """
        if inorder:
            index = inorder.index(preorder.pop(0))
            root = TreeNode(inorder[index])
            root.left = self.buildTree(preorder,inorder[0:index])
            root.right = self.buildTree(preorder,inorder[index+1:])
            return root
        

106. 从中序与后序遍历序列构造二叉树

class Solution(object):
    def buildTree(self, inorder, postorder):
        """
        :type inorder: List[int]
        :type postorder: List[int]
        :rtype: TreeNode
        """
        if inorder:
            root = TreeNode(postorder.pop())
            index = inorder.index(root.val)
            root.right = self.buildTree(inorder[index+1:],postorder)
            root.left = self.buildTree(inorder[:index],postorder)
            return root

109. 有序链表转换二叉搜索树

class Solution(object):
    def sortedListToBST(self, head):
        """
        :type head: ListNode
        :rtype: TreeNode
        """
        if not head:
            return 
        if not head.next:
            return TreeNode(head.val)
        slow,fast = head,head.next.next
        while fast and fast.next:
            fast = fast.next.next
            slow = slow.next
        tep = slow.next
        slow.next = None
        root = TreeNode(tep.val)
        root.left = self.sortedListToBST(head)
        root.right = self.sortedListToBST(tep.next)
        return root