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ConvertSortedListtoBinarySearchTree.cpp
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ConvertSortedListtoBinarySearchTree.cpp
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#include <vector>
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) {}
};
class Solution {
public:
/* Sol 0
* Just like a sorted array, we find the middle node of the list as the root node.
* Time complexity raise to O(nlogn)
* Does anybody have better solutions?
*/
TreeNode* sortedListToBST(ListNode* head) {
if(head == nullptr) return nullptr;
return sortedListToBST(head,nullptr);
}
// the tail here is not the same as my solution of the sorted array one, the tail is not valid.
TreeNode* sortedListToBST(ListNode *head,ListNode *tail){
if(head->next == tail) return new TreeNode(head->val);
ListNode *slow = head,*fast = head;
while(fast != tail && fast->next != tail){
slow = slow->next;
fast = fast->next->next;
}
TreeNode *node = new TreeNode(slow->val);
if(slow != head) node->left = sortedListToBST(head,slow);
if(slow->next != tail) node->right = sortedListToBST(slow->next,tail);
return node;
}
};