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。

 

相当于BFS

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