Convert Sorted List to Binary Search Tree

有序链表转平衡二叉搜索树

最新推荐文章于 2020-08-18 08:24:28 发布

原创最新推荐文章于 2020-08-18 08:24:28 发布 · 721 阅读

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本文介绍了一种将升序排列的单链表转换为高度平衡的二叉搜索树的方法。通过递归地查找中间节点作为根节点，并以此为基础构建左子树和右子树，最终形成一棵平衡的二叉搜索树。

Convert Sorted List to Binary Search Tree

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

package Tree;

/**
 * @Title: Convert_Sorted_List_to_Binary_Search_Tree.java
 * @Package Tree
 * @Description: TODO
 * @author nutc
 * @date 2013-9-1 下午2:46:08
 * @version V1.0
 */
public class Convert_Sorted_List_to_Binary_Search_Tree {
	public static void main(String args[]) {
		Convert_Sorted_List_to_Binary_Search_Tree l = new Convert_Sorted_List_to_Binary_Search_Tree();
		l.dos();
	}

	public void dos() {
		ListNode l1 = new ListNode(-1);
		ListNode l2 = new ListNode(0);
		ListNode l3 = new ListNode(1);
		ListNode l4 = new ListNode(2);
		l1.next = l2;
		l2.next = l3;
		l3.next = l4;
		sortedListToBST(l1);
	}

	 public TreeNode sortedListToBST(ListNode head) {
	        if(head ==null) return null;
	        ListNode end = head; 
	        int len = 0;
	        while(end!=null){
	            end= end.next;
	            len++;
	        }
	        
	        return find(head,len);
	    }
	    
	    public TreeNode find(ListNode start,int len){
	        //ListNode pre = null;
	        ListNode p1 =start;
	        //p2 = start;
	        if(start==null||len<=0)
	            return null;
	            
	        int mid = len/2;
	        for(int i=0;i<mid;i++){
	            p1 = p1.next;
	        }
	        /*
	        while(p2!=null && p2!=end){  //
	            pre = p1;
	            p1=p1.next;
	            p2=p2.next.next;
	        }*/
	        TreeNode node = new TreeNode(p1.val);
	        node.left = find(start,mid);
	        node.right = find(p1.next,len-mid-1);
	        return node;
	    }

	public class ListNode {
		int val;
		ListNode next;

		ListNode(int x) {
			val = x;
			next = null;
		}

	}

	public class TreeNode {
		int val;
		TreeNode left;
		TreeNode right;

		TreeNode(int x) {
			val = x;
		}
	}
}