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。

/*
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) {
        //层次遍历
        queue<TreeNode*> queue;
        vector<int> result;
        queue.push(root);
        if (root == NULL) {
            return result;
        }
        while (!queue.empty())
        {
            TreeNode* tmp_queue =queue.front();
            result.push_back(tmp_queue->val);
            if (tmp_queue->left != NULL) {
                queue.push(tmp_queue->left);
            }
            if (tmp_queue->right!=NULL) {
                queue.push(tmp_queue->right);
            }
            queue.pop();
            
        }
        return result;
    }
};