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