剑指offer 32：从上到下打印二叉树 II

/**
 * 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 {
    
    
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
    
    
        vector<vector<int>> res;
        queue<TreeNode*> que;
        if (root != nullptr) que.push(root);
        while (!que.empty()) {
    
    
            int n = que.size();
            vector<int> temp;
            for (int i = 0; i < n; ++i) {
    
    
                TreeNode* node = que.front();
                temp.push_back(node->val);
                que.pop();
                if (node->left != nullptr) que.push(node->left);
                if (node->right != nullptr) que.push(node->right);
            }
            res.push_back(temp);
        }
        return res;
    }
};