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;
}