LeetCode_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.
/** * 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 countNodeNumb(ListNode *head) { int count = 0; while(head) { count++; head = head->next; } return count ; } TreeNode * BST(ListNode *head, int size) { if(size == 1) return new TreeNode(head->val); int half = (size + 1 )/ 2; int count = 1; ListNode *pre, *p; pre = NULL; p = head; while(count < half) { pre = p; p = p->next; count ++ ; } TreeNode *Node = new TreeNode(p->val); Node->left = half-1 > 0 ? BST(head, half-1) : NULL ; Node->right = size - half > 0? BST(p->next, size - half) : NULL; return Node ; } TreeNode *sortedListToBST(ListNode *head) { // Start typing your C/C++ solution below // DO NOT write int main() function if(head == NULL) return NULL ; int size = countNodeNumb(head) ; TreeNode * myNode = BST(head, size); return myNode; } };
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