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  • leetcode__Convert Sorted List to Binary Search Tree

    Convert Sorted List to Binary Search Tree

     Total Accepted: 12283 Total Submissions: 45910My Submissions

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




    总结:这个是网上找的,还不明确为什么是以下这个样子,去掉&,就出错

    ListNode *&node


    TreeNode *sortedListToBST(ListNode *head)
    	{
    	    int len = 0;
            ListNode * node = head;
            while (node != NULL)
            {
                node = node->next;
                len++;
            }
            return buildTree(head, 0, len-1);
        }
        
        TreeNode *buildTree(ListNode *&node, int start, int end)
        {
            if (start > end) return NULL;
            int mid = start + (end - start)/2;
            TreeNode *left = buildTree(node, start, mid-1);
            TreeNode *root = new TreeNode(node->val);
            root->left = left;
            node = node->next;
            root->right = buildTree(node, mid+1, end);
            return root;
        }



    总结:这个開始的时候有点问题,改动了一下

    TreeNode *sortedListToBST(ListNode *head) 
    	{
    		vector<TreeNode*> treeNodes;
    		if(head == NULL) return NULL;
    		while (head != NULL)
    		{
    			TreeNode *node = new TreeNode(head->val);
    			treeNodes.push_back(node);
    			head = head->next;
    		}
    		return genBST(0, treeNodes.size()-1, treeNodes);
    }
    	
    	TreeNode* genBST(int start, int end, vector<TreeNode*> &treeNodes)
    	{
    		if (start == end) return treeNodes[start];
    		else if (start+1 == end)
    		{
    			treeNodes[start]->right = treeNodes[end];
    			return treeNodes[start];
    		} 
    
    		int mid = (start+end)/2;
    		TreeNode* root = treeNodes[mid];
    		root->left = genBST(start, mid-1, treeNodes);
    		root->right = genBST(mid+1, end, treeNodes);
    		return root;
    	}



    总结:上面这个代码跟我參考得到的思想一致,可是我的是time limit

    TreeNode *sortedListToBST(ListNode *head) {
    		int len = 0;
    		ListNode *node = head;
    		while(node)
    		{
    			len++;
    			node = node->next;
    		}
            return BuildTree(head,1,len);
    }
    
    	TreeNode *BuildTree(ListNode *node,int start,int end)
    	{
    		if(start > end) return NULL;
    		int mid = start + (end-start)/2;	
    		ListNode *mi_node = node;
    		for(int i=1;i<mid;i++)
    		{
    			mi_node = mi_node->next;
    		}
    
    		TreeNode *root = new TreeNode(mi_node->val); 
    		root->left = BuildTree(node,start,mid-1);
    		root->right = BuildTree(node,mid+1,end);
    		return root;
    	}





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  • 原文地址:https://www.cnblogs.com/zfyouxi/p/3875754.html
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