C++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(牛客剑指offer)

/*
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> result;
        if(root==NULL)return result;
        Q.push(root);
        while(!Q.empty())
        {
         	TreeNode* p = Q.front();
            Q.pop();
            result.push_back(p->val);
            if(p->left!=NULL)
                Q.push(p->left);
            if(p->right!=NULL)
                Q.push(p->right);
        }
        return result;
	}
};