LeetCode 剑指 Offer 32 - II. 从上到下打印二叉树 II

解法一（队列）：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    queue<TreeNode*> q;
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> rst;
        if (root) {
            q.push(root);
            while (!q.empty()) {
                vector<int> temp {};
                int curNodeNum = (int)q.size();
                for (int i = 0; i < curNodeNum; ++i) {
                    TreeNode* p = q.front();
                    q.pop();
                    temp.emplace_back(p->val);
                    if (p->left) q.push(p->left);
                    if (p->right) q.push(p->right);
                }
                rst.emplace_back(temp);
            }
        }
        return rst;
    }
};

解法二：