Question Definition
Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST. For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
Example:
Given the sorted linked list: [-10,-3,0,5,9],
One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:
0
/ \
-3 9
/ /
-10 5
Java Solution
public TreeNode sortedListToBST(ListNode head) {
if(head==null)
return null;
return toBST(head,null);
}
public TreeNode toBST(ListNode head, ListNode tail){
ListNode slow = head;
ListNode fast = head;
if(head==tail) return null;
while(fast!=tail&&fast.next!=tail){
fast = fast.next.next;
slow = slow.next;
}
TreeNode thead = new TreeNode(slow.val);
thead.left = toBST(head,slow);
thead.right = toBST(slow.next,tail);
return thead;
}
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