public class ConvertSortedListToBinarySearchTree {

public static TreeNodeI sortedListToBST(ListNode head) {

if(head==null){

return null;

}

if(head.next==null){

return new TreeNodeI(head.val);

}

ListNode last =head;

ListNode mid = head;

ListNode runner = head;

while(runner.next!=null){

runner=runner.next.next;

last = mid;

mid = mid.next;

if(runner==null){

break;

}

}

TreeNodeI root = new TreeNodeI(mid.val);

ListNode right = mid.next;

root.right = sortedListToBST(right);

last.next = null;

ListNode left = head;

root.left = sortedListToBST(left);

return root;

}

public static void main(String args[]){

ListNode head = new ListNode(1);

head.next = new ListNode(2);

head.next.next = new ListNode(3);

head.next.next.next = new ListNode(4);

head.next.next.next.next = new ListNode(5);

head.next.next.next.next.next = new ListNode(6);

TreeNodeI root = sortedListToBST(head);

root.preorderPrint(root);

}

}