Leetcode Populating Next Right Pointers in Each Node II

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

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写代码时陷入了各种复杂情况的判断，写的举步维艰。后面参考了下别人的代码，发现通过使用哨兵节点，可以很大的简化复杂度，写简洁优雅代码真是技巧性的活。

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) {        while(root)          {              TreeLinkNode* temp = new TreeLinkNode(0);            TreeLinkNode* cur = temp;            while(root)              {                if(root->left != NULL)                {                    cur->next = root->left;                    cur = cur->next;                }                if(root->right != NULL)                {                    cur->next = root->right;                    cur = cur->next;                }                root = root->next;            }                          root = temp->next;            temp->next = NULL;            delete temp;        }      }};