leetcode #116 in cpp

Solution:

perform BFS to traverse the tree level by level using a queue. For each level, pop current front node,  link the node's next to the new front node in the queue.

Code:

/**
 * 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*> que;
        que.push_back(root);
        while(!que.empty()){
            int cap = que.size();
            que.push_back(NULL);
            while(cap > 0){
                TreeLinkNode *temp = que.front();
                que.pop_front();
                temp->next = que.front();
                if(temp->left){
                    que.push_back(temp->left);
                    que.push_back(temp->right);
                }
                cap--;
            }
            que.pop_front();//pop the null at the front
        }
        return;
    }
};