class TreeNode {

int val;

TreeNode left;

TreeNode right;

TreeNode(int x){val = x;}

}

class ListNode {

int val;

ListNode next;

public ListNode(int val) {

this.val = val;

}

}

class ListNodeTools {

public static ListNode getListNode(int[] nums) {

ListNode dummy = new ListNode(-1);

ListNode pre = dummy;

for (int num : nums) {

pre.next = new ListNode(num);

pre = pre.next;

}

return dummy.next;

}

public static void printListNode(ListNode node) {

String s = "";

ListNode p = node;

while (p != null) {

s += p.val + "->";

p = p.next;

}

System.out.println(s+"null");

}

}