Populating Next Right Pointers in Each Node-优快云博客

本文介绍了一种在常数额外空间内实现完全二叉树节点连接的算法。通过递归方式设置每个节点的next指针指向其右侧相邻节点，若无相邻节点则设置为NULL。此算法适用于所有叶子节点在同一层级且每个父节点都有两个子节点的完美二叉树。

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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 toNULL.

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

既然题目非要说完全二叉树，那就按照完全来做

/**
 * 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 || root.left == null) {
            return;
        }
        
        root.left.next = root.right;
        if (root.next == null) {
            root.right.next = null;
        } else {
            root.right.next = root.next.left;
        }
        
        connect(root.left);
        connect(root.right);
    }
}