"Leetcode-Interview algorithm classic-java Implementation" "109-convert Sorted List to Binary Search tree (sort list converted to binary sort tree)"

109-convert Sorted list to binary Search tree (sort list converted to binary sort tree) "leetcode-Interview algorithm classic-java Implementation" "All topics Directory Index" Original Question

Given a singly linked list where elements is sorted in ascending order, convert it to a height balanced BST.

Main Topic

Given an ascending single-linked list, convert it to a highly balanced two-fork tree

Thinking of solving problems

Solution One: The value of the single-linked list into an array, through the array to build a binary tree, the algorithm time complexity is: O (n), the spatial complexity is: O (n)
Solution Two: The recursive method is used,
(a) Find the middle node, build the root node,
(ii) the left half of the middle node constructs the left sub-tree,
(iii) Right sub-tree of middle node construction
The second method of solving the problem

Code Implementation

Tree Node class

publicclass TreeNode {    int val;    TreeNode left;    TreeNode right;    TreeNode(int x) { val = x; }}

Algorithm implementation class

 Public classSolution { PublicTreeNodeSortedlisttobst(ListNode head) {//If the list is empty, return null directly        if(Head = =NULL) {return NULL; }//list has only one node.        if(Head.next = =NULL) {return NewTreeNode (Head.val); }//Fast moving nodes, two positions per moveListNode fast = Head.next.next;//Record intermediate nodesListNode mid = head;//Find the middle node.         while(Fast! =NULL&& Fast.next! =NULL) {mid = Mid.next;        Fast = Fast.next.next; }//With the next node of the middle node as the root node .TreeNode root =NewTreeNode (Mid.next.val);//Build Right sub-treeRoot.right = Sortedlisttobst (Mid.next.next);//Record list of points to be brokenListNode midnext = Mid.next;//Disconnect single-linked list (destroys the structure of the original single-linked list)Mid.next =NULL;//Build left subtreeRoot.left = Sortedlisttobst (head);//re-connect the linked list.Mid.next = Midnext;//Return results        returnRoot }}

Evaluation Results

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"Leetcode-Interview algorithm classic-java Implementation" "109-convert Sorted List to Binary Search tree (sort list converted to binary sort tree)"