Solution.java

/**
 * 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) {
        if (root!=null) {
            TreeLinkNode rootNext=root.next;
            TreeLinkNode sonNext=null;
            while (rootNext!=null&&sonNext==null) {
                if (rootNext.left!=null) {
                    sonNext=rootNext.left;
                }else {
                    sonNext=rootNext.right;
                }
                rootNext=rootNext.next;
            }
            if (root.left!=null) {
                if (root.right!=null) {
                    root.left.next=root.right;
                }else {
                    root.left.next=sonNext;
                }
            }
            if (root.right!=null) {
                root.right.next=sonNext;
            }
            connect(root.right);
            connect(root.left);
        }
    }
}