//無向圖的關鍵邊,dfs鄰接陣形式,O(n^2)
//返回關鍵邊條數,key[][2]返回邊集
//傳入圖的大小n和鄰接陣mat,不相鄰點邊權0
#define MAXN 100

void search(int n,int mat[][MAXN],int* dfn,int* low,int now,int& cnt,int key[][2]){
	int i;
	for (low[now]=dfn[now],i=0;i<n;i++)
		if (mat[now][i]){
			if (!dfn[i]){
				dfn[i]=dfn[now]+1;
				search(n,mat,dfn,low,i,cnt,key);
				if (low[i]>dfn[now])
					key[cnt][0]=i,key[cnt++][1]=now;
				if (low[i]<low[now])
					low[now]=low[i];
			}
			else if (dfn[i]<dfn[now]-1&&dfn[i]<low[now])
				low[now]=lev[i];
		}
}

int key_edge(int n,int mat[][MAXN],int key[][2]){
	int ret=0,i,dfn[MAXN],low[MAXN];
	for (i=0;i<n;dfn[i++]=0);
	for (i=0;i<n;i++)
		if (!dfn[i])
			dfn[i]=1,bridge(n,mat,dfn,low,i,ret,key);
	return ret;
}