117. 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    7After calling your function, the tree should look like:         1 -> NULL       /  \      2 -> 3 -> NULL     / \    \    4-> 5 -> 7 -> NULL*//** * 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;        TreeLinkNode *pre=NULL;//下一行中当前节点的前一个节点        TreeLinkNode *headL=NULL;//下一行的从左边第一个非空节点        TreeLinkNode *cur=root;        while(cur)        {            while(cur)            {                if(cur->left){                    if(pre==NULL){                        headL=cur->left;                    }else{                        pre->next=cur->left;                    }                    pre=cur->left;                }                if(cur->right){                    if(pre==NULL){                        headL=cur->right;                    }else{                        pre->next=cur->right;                    }                    pre=cur->right;                }                cur=cur->next;            }            cur=headL;            headL=NULL;            pre=NULL;        }    }};