LeetCode - Populating Next Right Pointers in Each Node II

題目：

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    7

After calling your function, the tree should look like:

         1 -> NULL
       /  \
      2 -> 3 -> NULL
     / \    \
    4-> 5 -> 7 -> NULL

思路：

遞歸，對root的左右進行連接操作，然後先遞歸右樹，再遞歸左樹。

package tree;

public class PopulatingNextRightPointersInEachNodeII {

    public void connect(TreeLinkNode root) {
        if (root == null || (root.left == null && root.right == null)) return;

        TreeLinkNode next = root.next;
        while (next != null) {
            if(next.left != null) {
                next = next.left;
                break;
            }
            
            if (next.right != null) {
                next = next.right;
                break;
            }
            
            next = next.next;
        }
        
        if (root.right != null) 
            root.right.next = next;
         
        if (root.left != null)
            root.left.next = root.right == null ? next : root.right;
                
        connect(root.right);
        connect(root.left);
    }

}