Convert Sorted List to Binary Search Tree

最新推荐文章于 2020-08-18 08:24:28 发布

desmondbcfntu

最新推荐文章于 2020-08-18 08:24:28 发布

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分类专栏： LeetCode

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

题目解析：

将整个过程看作是求取链表的中值

#include <iostream>

using namespace std;

struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

ListNode *getMid(ListNode *head)
{
	if(head == NULL)
		return NULL;
	if(head->next == NULL)
	{
		return head;
	}

	ListNode *midAft = NULL;
	ListNode *mid = head;
	ListNode *midPre = head->next->next;

	while(midPre != NULL)
	{
		midAft = mid;
		mid = mid->next;
		midPre = midPre->next;
		if(midPre == NULL)
			break;
		midPre = midPre->next;
	}
	if(midAft !=NULL)
		midAft->next = NULL;
	return mid;
}

TreeNode *sortedListToBST(ListNode *head) {
	TreeNode *root;
	if(head == NULL)
		return NULL;

	ListNode *mid = getMid(head);
	root = (TreeNode *)malloc(sizeof(TreeNode));
	root->val = mid->val;

	ListNode *leftTree;
	ListNode *rightTree;
	if(mid == head)
		leftTree = NULL;
	else
		leftTree = head;

	rightTree = mid->next;

	root->left = sortedListToBST(leftTree);
	root->right = sortedListToBST(rightTree);

	return root;
}


int main(void)
{

	system("pause");
	return 0;
}