题解 | #从上往下打印二叉树#

class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
		if(root==NULL) return {};
		vector<int> res; //存储结果
		queue<TreeNode*> que; //队列实现BFS
		que.push(root);
		while(que.size()!=0){
			res.push_back(que.front()->val);   //队头值进入res
			if(que.front()->left!=NULL) que.push(que.front()->left);  //左右不空就进入队列
			if(que.front()->right!=NULL) que.push(que.front()->right);
			que.pop();  //当前队头出队
		}
		return res;
    }
};