Bloomberg 面试题05012012[2]

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本文介绍如何使用C++实现二叉树的层次遍历，从根节点开始，逐层打印每个节点的值。

You have a binary tree. Print node values starting from the root going level by level, i.e. first line has root node's value, second line has two child node's values, third line - left and right child nodes values of the root's left child then left and right child nodes values of the root's right child, and so on.

#include <iostream>
#include <queue>

struct node
{
	int data;
	node* left;
	node* right;
	node(int _data, node* _left, node* _right)
	{
		data = _data;
		left = _left;
		right = _right;
	}
};



int main()
{
	node* n7 = new node(7, NULL, NULL);
	node* n6 = new node(6, NULL, NULL);
	node* n5 = new node(5, NULL, NULL);
	node* n4 = new node(4, NULL, NULL);
	node* n3 = new node(3, n6, n7);
	node* n2 = new node(2, n4, n5);
	node* n1 = new node(1, n2, n3);
	node* root = n1;

	std::queue<node*> q;
	q.push(root);
	q.push(NULL);

	while(!q.empty())
	{
		node* cur = q.front();
		if(cur != NULL)
		{
			printf("%d ", cur->data);
			q.pop();
			if(cur->left != NULL)
				q.push(cur->left);
			if(cur->right != NULL)
				q.push(cur->right);
		}
		else
		{
			if(q.size() == 1)
				break;
			else
			{
				q.pop();
				q.push(NULL);
				printf("\n");
			}
		}
	}

	return 0;

}