【PAT Advanced Level】1004. Counting Leaves (30)

利用广度优先搜索，找出每层的叶子节点的个数。

#include <iostream>

#include <vector>

#include <queue>

#include <fstream>

using namespace std;



vector<vector<int>> tree;

vector<int> ans;



void BFS(int s)

{

	queue<pair<int, int>> q;

	q.push(make_pair(s, 0));

	int cur_step = 0;

	int cnt = 0;



	while (!q.empty())

	{

		int id = q.front().first;

		int step = q.front().second;

		q.pop();

		if(step > cur_step)

		{

			cur_step = step;

			ans.push_back(cnt);

			cnt = 0;

		}

		if(tree[id].size() == 0) cnt++;

		for(int i = 0; i < tree[id].size(); i++)

			q.push(make_pair(tree[id][i], step + 1));

	}

	ans.push_back(cnt);

	return;

}



int main()

{

	//fstream cin("a.txt");



	int N, M;

	cin>>N>>M;

	tree.resize(N + 1);

	for(int i = 0; i < M; i++)

	{

		int id, num;

		cin>>id>>num;

		while (num--)

		{

			int tmp;

			cin>>tmp;

			tree[id].push_back(tmp);

		}

	}

	BFS(1);

	for(int i = 0; i < ans.size(); i++)

	{

		if(i == 0)

			cout<<ans[i];

		else

			cout<<" "<<ans[i];

	}

	cout<<endl;

}