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文章目录
  1. 1. Convert Sorted List to Binary Search Tree
    1. 1.1. 题目
    2. 1.2. 思路
    3. 1.3. 解题

Convert Sorted List to Binary Search Tree

题目

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

思路

取链表的中间结点做为根节点，该结点前面的链表部分做为左子树，结点后面的部分做为右子树。然后利用递归的思想，不断递归左子树和右子树。

解题

c++版

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/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int calLen(ListNode *node)
    {
        int len = 0;
        while(node)
        {
            len++;
            node = node->next;
        }
        return len;
    }
    
    TreeNode *createTree(ListNode *node, int left, int right)
    {
        if (left > right)
            return NULL;
            
        int mid = (left + right) / 2;
        
        ListNode *p = node;
        
        for(int i = left; i < mid; i++)
            p = p->next;
            
        TreeNode *leftNode = createTree(node, left, mid - 1);
        TreeNode *rightNode = createTree(p->next, mid + 1, right);
        
        TreeNode *tNode = new TreeNode(p->val);
        
        tNode->left = leftNode;
        tNode->right = rightNode;
        
        return tNode;        
    }
    
    TreeNode *sortedListToBST(ListNode *head) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int len = calLen(head);
        return createTree(head, 0, len - 1);
    }
};

python 版

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# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    # @param {ListNode} head
    # @return {TreeNode}
    def sortedListToBST(self, head):
        len=self.calLen(head)
        return self.createTree(head,0,len-1)
        
    def calLen(self,head):
        len=0
        cur=head
        while(cur):
            cur=cur.next
            len+=1
        return len
    
    def createTree(self,head,left,right):
        if left>right:
            return None
        mid=(left+right)/2
        p=head
        for i in range(left,mid):
            p=p.next
        leftNode=self.createTree(head,left,mid-1)
        rightNode=self.createTree(p.next,mid+1,right)
        tNode=TreeNode(p.val)
        tNode.left=leftNode
        tNode.right=rightNode
        return tNode
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文章目录
  1. 1. Convert Sorted List to Binary Search Tree
    1. 1.1. 题目
    2. 1.2. 思路
    3. 1.3. 解题