[Leetcode] Populating Next Right Pointers in Each Node II

/**
 * 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*> q;
        q.push(root);
        q.push(NULL);
        
        while (!q.empty())
        {
            TreeLinkNode* cur = q.front();
            q.pop();
            if (cur)
            {
                cur->next = q.front();
                
                if (cur->left) q.push(cur->left);
                if (cur->right) q.push(cur->right);
            }
            else
            {
                if (q.empty())
                    break;
                q.push(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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (!root) return;
        
        TreeLinkNode* cur = root->next;
        TreeLinkNode* p = NULL;
        while (cur)
        {
            if (cur->left)
            {
                p = cur->left;
                break;
            }
            if (cur->right)
            {
                p = cur->right;
                break;
            }
            cur = cur->next;
        }
        
        if (root->right)
            root->right->next = p;
        
        if (root->left)
            root->left->next = root->right ? root->right: p;
        
        connect(root->right);
        connect(root->left);
    }
};