117_connectTreeLinkNode2.java

//This dummy head is awesome!!!!


/**
 * 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 dummy = new TreeLinkNode(0);
        TreeLinkNode pre = dummy;
        while(root!=null){
            if(root.left!=null){
                pre.next = root.left;
                pre = pre.next;
            }
            if(root.right!=null){
                pre.next = root.right;
                pre = pre.next;
            }
            root = root.next; //dont forget!!!
            if(root == null){
                root = dummy.next;
                pre = dummy;
                dummy.next = null;
            }
        }
    }
}