C++版 - 剑指offer 面试题23：从上往下打印二叉树(二叉树的层次遍历BFS) 题解

#include<cstdio>
#include<vector>
#include<queue>
using namespace std;

struct TreeNode
{
	int val;
	TreeNode *left, *right;
	TreeNode(int x): val(x), left(NULL), right(NULL) {} 
};
class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode *root){
	vector<int> res(0);
    if(root==NULL) return res;
	
	queue<TreeNode*> q;	
	q.push(root);
	
	while(!q.empty()) 
	{
		TreeNode *p= q.front();
		res.push_back(p->val);
		q.pop();
		if(p->left != NULL) q.push(p->left);
		if(p->right != NULL) q.push(p->right);
	}
	return res;
    }     

};
// 以下为测试 
int main()
{
	Solution sol;
	vector<int> res;
	
	TreeNode *root = new TreeNode(1); 
    root->right = new TreeNode(2); 
    root->right->left = new TreeNode(3); 
	
	res=sol.PrintFromTopToBottom(root);
	
	for(int i:res)
		printf("%d ",i);  // 此处为vector遍历的方法，C++11标准支持 
	return 0;
}