面試題32.1 從上往下打印二叉樹

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