Populating Next Right Pointers in Each Node (I & II)

题目：Populating Next Right Pointers in Each Node (I & II)

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

思路

这就相当于 对任意的二叉树进行层次遍历，然后将queue中相邻的两个节点通过next链接起来，so easy ！

算法类似于前面讲的  Binary Tree Level Order Traversal

代码如下：

/** * Definition for binary tree with next pointer. * struct TreeLinkNode { *  int val; *  TreeLinkNode *left, *right, *next; *  TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {} * }; */class Solution {public:    void connect(TreeLinkNode *root) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if(!root)            return ;        queue<TreeLinkNode *> myqueue;        myqueue.push(root);        myqueue.push(NULL);        TreeLinkNode * tmp = myqueue.front();        myqueue.pop();        while(!myqueue.empty())        {            if(tmp!=NULL)            {                if(tmp->left!=NULL)                    myqueue.push(tmp->left);                if(tmp->right!=NULL)                    myqueue.push(tmp->right);                tmp->next = myqueue.front();                myqueue.pop();                tmp = tmp->next;            }            else            {                myqueue.push(NULL);                tmp = myqueue.front();                myqueue.pop();            }                    }                }};

最新：

/** * 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) {        Queue<TreeLinkNode> queue = new LinkedList<TreeLinkNode>();        if(root == null) {            return ;        }        queue.offer(root);        queue.offer(null);        while (queue.size() > 0) {           TreeLinkNode cur = queue.poll();           if(cur == null) {               if(queue.size() > 0){   //此处的判断，是为了出现队列中出现 null 异常                    queue.offer(null);               }               continue;           }           cur.next = queue.peek();           if(cur.left != null) {               queue.offer(cur.left);           }           if(cur.right != null) {               queue.offer(cur.right);           }        }    }}