116. Populating Next Right Pointers in Each Node && 117. II-优快云博客

本文介绍了一种常量额外空间复杂度下填充二叉树节点指针的方法，使其能够指向其右侧相邻节点，适用于完美二叉树。并讨论了扩展至一般二叉树时的解决方案。

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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 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,
1
/ \
2 3
/ \ / \
4 5 6 7
After calling your function, the tree should look like:
1 -> NULL
/ \
2 -> 3 -> NULL
/ \ / \
4->5->6->7 -> NULL
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层序遍历，利用next指针进行层序遍历

public void connect(TreeLinkNode root) {
        if(root == null) return;
        TreeLinkNode level = root;
        while(level.left != null){
            TreeLinkNode cur = level;
            while(cur != null){
                if(cur.left != null) cur.left.next = cur.right;
                if(cur.right != null && cur.next != null) cur.right.next = cur.next.left;
                cur = cur.next;
            }
            level = level.left;
        }

Follow up for problem “Populating Next Right Pointers in Each Node”.

What if the given tree could be any binary tree? Would your previous solution still work?

Note:

You may only use constant extra space.

public void connect(TreeLinkNode root) {
        if(root == null) return;
        if(root.left == null && root.right == null) return;
        TreeLinkNode p = root;
        TreeLinkNode fake = new TreeLinkNode(0),pre = fake;
        while(p != null){
           if(p.left != null){
               pre.next = p.left;
               pre = pre.next;
           }
           if(p.right != null){
               pre.next = p.right;
               pre = pre.next;
           }
           p = p.next;
           if(p == null){        //层序遍历，下一层
               p = fake.next;
               pre = fake;
               fake.next = null;
           }
        }
    }