从上往下打印二叉树

+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。

• 层次遍历
• C++ 代码

/*
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) {
        if(!root) return {};
        vector <int> vec;
        queue<TreeNode *> q;
        st.push(root);
        while(!st.empty())
        {
            TreeNode* tmp=q.front();
            vec.push_back(tmp->val);
            st.pop();
            if(tmp->left) q.push(tmp->left);
            if(tmp->right) q.push(tmp->right);
        }
        return vec;
    }
};