从上往下打印二叉树

题目描述

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。

​​https://www.nowcoder.com/practice/7fe2212963db4790b57431d9ed259701?tpId=13&tqId=11175&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking​​

题解：

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