【Populating Next Right Pointers in Each Node II】cpp

题目：

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.

For example,
Given the following binary tree,

         1
       /        2    3
     / \        4   5    7

After calling your function, the tree should look like:

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

代码：

/**
 * 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) {
            if (!root) return;
            deque<TreeLinkNode *> curr, next;
            curr.push_back(root);
            while ( !curr.empty() )
            {
                TreeLinkNode dummy(-1);
                TreeLinkNode *pre = &dummy;
                while ( !curr.empty() )
                {
                    TreeLinkNode *tmp = curr.front(); curr.pop_front();
                    pre->next = tmp;
                    if (tmp->left) next.push_back(tmp->left);
                    if (tmp->right) next.push_back(tmp->right);
                    pre = tmp;
                }
                pre->next = NULL;
                std::swap(curr, next);
            }
    }
};

tips：

广搜思路（有些违规，因为不是const extra space）

每一层设立一个虚拟头结点，出队的同时pre->next = tmp