从上往下打印二叉树

/*
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) {

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