图的根节点-数据结构作业。。

 

 

手写邻接表 BFS

 

#include <iostream>

#include <queue>

using namespace std;



const int maxn = 100000;

const int maxm = 300000;

struct Graph {

	int NE , NV;

	int head[maxn];

	struct Node{

		int next , v;

		Node(){}

		Node(int a,int b):v(a) , next(b){}

	}E[maxm];

	void clear(int n) {

		NV = n;

		NE = 0;

		memset(head,-1,sizeof(int)*n);

	}

	inline void Insert(int u,int v) {

		E[NE] = Node(v , head[u]);

		head[u] = NE ++;

	}

	void Print() {

		for(int i = 0 ; i < NV ; i ++) {

			printf("%d:",i);

			for(int j = head[i]; j != -1; j = E[j].next){

				printf(" %d",E[j].v);

			}

			puts("");

		}

	}

}G;



int n, m, ctr;

int visit[maxn]; 



void BFS(int cur) {

	queue<int> Q;

	Q.push(cur);

	visit[cur] = 1;

	while( !Q.empty() ){

		for(int i = G.head[Q.front()]; i != -1; i = G.E[i].next ){

			if(!visit[G.E[i].v]){

				visit[G.E[i].v] = 1;

				Q.push(G.E[i].v);

				ctr++;

				if(ctr >= n - 1) printf("%d为根节点\n", cur);

			}

		}

		Q.pop();

	}

}







int main(){

	cin >> n;//读入顶点数 

	G.clear(n);

	cin >> m;//读入边数

	int begin, end;

	for(int i = 0; i < m; ++i) {

		scanf("%d %d", &begin, &end);

		G.Insert(begin, end);

	}

	//遍历图 输出根节点

	for(int i = 0; i < n; ++i){

		memset(visit, 0, sizeof(visit));

		ctr = 0;

		BFS(i);

	}

	return 0;

}