LeetCode Populating Next Right Pointers in Each Node II

原题链接在这里：https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/

本题是Populating Next Right Pointers in Each Node的进阶版。关键是在有null的时候如何找到下一节点，通过while loop找到next节点，while loop 很关键。

Note: 1. 递归时先递归右子树，后递归左子树，否则会出错。

2. while loop中要加break, 否则会infinite loop.

AC 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){
            return;
        }
        TreeLinkNode next = null;
        TreeLinkNode rootNext = root.next;
        while(rootNext != null){
            if(rootNext.left != null){
                next = rootNext.left;
                break;
            }else if(rootNext.right != null){
                next = rootNext.right;
                break;
            }else{
                rootNext = rootNext.next;
            }
        }
        if(root.right != null){
            root.right.next = next;
        }
        if(root.left != null){
            if(root.right != null){
                root.left.next = root.right;
            }else{
                root.left.next = next;
            }
        }
        connect(root.right);
        connect(root.left);
    }
}