剑指Offer---从上到下打印二叉树

题目：从上到下打印出二叉树的每个结点，同一层结点按照从左到右的顺序打印。
这道题的实质是二叉树的层序遍历，借助队列来实现。

#include <queue>
class Solution {
public:
    vector<vector<int> > Print(TreeNode* pRoot) {
        vector<vector<int> > v;
        if (pRoot == NULL)
            return v;

        queue<TreeNode*> q;
        q.push(pRoot);

        while (!q.empty())
        {
            int size = q.size();
            vector<int> tmp;

            for (int i = 0; i < size; ++i)
            {
                TreeNode* pCur = q.front();
                tmp.push_back(pCur->val);

                if (pCur->left)
                    q.push(pCur->left);
                if (pCur->right)
                    q.push(pCur->right);

                q.pop();
            }
            v.push_back(tmp);
        }
        return v;
    }
};