题解 | #从上往下打印二叉树#

1. 定义队列处理二叉树

queue<TreeNode*> que;
if (root != NULL) que.push(root);

2. 遍历存储每层结果

        while (!que.empty()) {
            int size = que.size();
            for (int i = 0; i < size; i++) {
                TreeNode* node = que.front();
                que.pop();
                result.push_back(node->val);
                if (node->left) que.push(node->left);
                if (node->right) que.push(node->right);
            }
        }