判斷無向圖是否是一顆樹

 

思路：

無向圖是樹的條件是有n-1條邊的連通圖

int visit[MAXV];
void DFS2(AdjGraph *G, int v, int &vn, int &en){
	visit[v] = 1;
	vn++;
	ArcNode *p = G->adjlist[v].firstarc;
	while(p != NULL){
		en++;//注意此句寫在if外面 
		if(visit[p->no] == 0){
			
			DFS2(G, p->no, vn, en);
		}	
		p = p->nextarc;
	}
}

int GisTree(AdjGraph *G){
	int vn = 0, en = 0;
	for(int i = 0; i < G->n; ++i) visit[i] = 0;
	DFS2(G, 1, vn, en);
	cout << vn << " " << en << endl;
	if(vn == G->n && en/2 == G->n-1) return 1;
	else return 0;
}