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);    }}