Practice12：从上往下打印出二叉树的每个节点，同层节点从左至右打印

Practice12：

从上往下打印出二叉树的每个节点，同层节点从左至右打印。

S1:

牛客题解之一：

取队列为中间变量，先入先出

/*
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};*/
class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
        vector<int> res;
        if(!root)return res;
		queue<TreeNode*> q;
		q.push(root);
		while (!q.empty()) {
			TreeNode* mid = q.front();
			res.push_back(mid->val);
			q.pop();
			if (mid->left)q.push(mid->left);
			if(mid->right)q.push(mid->right);
		}
		return res;
    }
};