题目描述：

Given a binary tree

    struct TreeLinkNode {
      TreeLinkNode *left;
      TreeLinkNode *right;
      TreeLinkNode *next;
    }

Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL.

Initially, all next pointers are set to NULL.

Note:

You may only use constant extra space. You may assume that it is a perfect binary tree (ie, all leaves are at the same level, and every parent has two children).

For example, Given the following perfect binary tree,

After calling your function, the tree should look like:

         1 -> NULL
       /  \
      2 -> 3 -> NULL
     / \  / \
    4->5->6->7 -> NULL

思路：

本题自然要想到二叉树的层序遍历。

注意右孩子的下一节点的情况，它有可能是 null ，也有可能是其父节点的下一节点的左孩子。

代码实现：

/**
 * 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;
        }
        if(root.left!=null){
            root.left.next = root.right;
        }
        if(root.right!=null){
            root.right.next = root.next!=null?root.next.left:null;
        }
            
        connect(root.left);
        connect(root.right);
    }
}

【LeetCode】116. Populating Next Right Pointers in Each Node

题目描述：

思路：

代码实现：