剑指offer-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> out;
        if(root==NULL)
            return out;
        queue<TreeNode*> Q;  //要注意加*
        Q.push(root);
        while(!Q.empty()){
            TreeNode* p = Q.front();
            out.push_back(p->val);
            Q.pop();
            if(p->left!=NULL)
                Q.push(p->left);
            if(p->right!=NULL)
                Q.push(p->right);
        }
        return out;
    }
};