思路

典型的层次遍历，套模板即可。

代码实现

/*
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};*/
//其实就是树的层次遍历
class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
    	vector<int>ans;
    	queue<TreeNode*>q;
    	if(root==nullptr) return ans;
    	q.push(root);
    	while(!q.empty())
    	{	
    		TreeNode *node = q.front();
    		q.pop();
    		ans.push_back(node->val);
    		if(node->left) q.push(node->left);
    		if(node->right) q.push(node->right);
    	}
    	return ans;
    }
};