给定一颗完全二叉树，给每一层添加上next的指针，从左边指向右边

void Solution::yahooTree(TreeNode *root)
{
    if (root == NULL)
        return;
    TreeNode *p = root;
    root->next = NULL;
    TreeNode *tmp = root->left;
    while(p){
        if (p->right!=NULL){
            if (p->next!=NULL){
                p->right->next = NULL;
                p->left->next = p->right;
            }else{
                p->right->next = p->next->left;
                p->left->next = p->right;
            }
        }else if (p->left!=NULL){
            p->left->right = NULL;
        }
        p = p->next;
        if (p == NULL){
            if (tmp!=NULL)){
                p = tmp;
                tmp = tmp->left;
            }else{
                return ;
            }
        }
    }
}