convert-sorted-list-to-binary-search-tree

Posted 2020-07-09 Adding

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

public class Solution {
    public TreeNode sortedListToBST(ListNode head) {
        int len=lenOFlist(head);
         TreeNode root=creatTree(head,0,len-1);
        return root;
        
    }
    public TreeNode creatTree(ListNode head,int left,int right){
        if(left>right)return null;
        int mid=(right+left+1)/2;/// right-(right-left+1)/2
        ListNode p=head;
        for (int i = left; i < mid; i++) {
            p=p.next;
        }
        TreeNode node=new TreeNode(p.val);
        TreeNode leftTree=creatTree(head, left, mid-1);
        TreeNode rightTree=creatTree(p.next, mid+1, right);
        node.left=leftTree;
        node.right=rightTree;
        
        return node;
        
    }
    public int lenOFlist(ListNode head){
        ListNode p=head;
        int count = 0;
        while(p!=null){
            count++;
            p=p.next;
        }
        return count;
    }
    
}