Follow up for problem “Populating Next Right Pointers in Each Node”.

What if the given tree could be any binary tree? Would your previous solution still work?

Note:

You may only use constant extra space.
For example,
Given the following binary tree,

1
2
3
4
5
     1
   /  \
  2    3
 / \    \
4   5    7

After calling your function, the tree should look like:

1
2
3
4
5
     1 -> NULL
   /  \
  2 -> 3 -> NULL
 / \    \
4-> 5 -> 7 -> NULL
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/**
 * Definition for binary tree with next pointer.
 * public class TreeLinkNode {
 *     int val;
 *     TreeLinkNode left, right, next;
 *     TreeLinkNode(int x) { val = x; }
 * }
 */
public class Solution {
    public void connect(TreeLinkNode root) {
        TreeLinkNode cur = root; // current node in the upper level
        TreeLinkNode head = null; // left most node in the lower level
        TreeLinkNode prev = null; // previous node in the same level
        
        while (cur != null) {
            while (cur != null) {
                if (cur.left != null) {
                    if (prev != null) {
                        prev.next = cur.left;
                    } else {
                        head = cur.left;
                    }
                    prev = cur.left;
                }
                if (cur.right != null) {
                    if (prev != null) {
                        prev.next = cur.right;
                    } else {
                        head = cur.right;
                    }
                    prev = cur.right;
                }
                cur = cur.next;
            }
            cur = head;
            prev = null;
            head = null;
        }
    }
}