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  • POJ 1144 Network

    Network

    Time Limit: 1000MS

     

    Memory Limit: 10000K

    Total Submissions: 13138

     

    Accepted: 6009

    Description

    A Telephone Line Company (TLC) is establishing a new telephone cable network. They are connecting several places numbered by integers from 1 to N . No two places have the same number. The lines are bidirectional and always connect together two places and in each place the lines end in a telephone exchange. There is one telephone exchange in each place. From each place it is 
    possible to reach through lines every other place, however it need not be a direct connection, it can go through several exchanges. From time to time the power supply fails at a place and then the exchange does not operate. The officials from TLC realized that in such a case it can happen that besides the fact that the place with the failure is unreachable, this can also cause that some other places cannot connect to each other. In such a case we will say the place (where the failure 
    occured) is critical. Now the officials are trying to write a program for finding the number of all such critical places. Help them.

    Input

    The input file consists of several blocks of lines. Each block describes one network. In the first line of each block there is the number of places N < 100. Each of the next at most N lines contains the number of a place followed by the numbers of some places to which there is a direct line from this place. These at most N lines completely describe the network, i.e., each direct connection of two places in the network is contained at least in one row. All numbers in one line are separated 
    by one space. Each block ends with a line containing just 0. The last block has only one line with N = 0;

    Output

    The output contains for each block except the last in the input file one line containing the number of critical places.

    Sample Input

    5

    5 1 2 3 4

    0

    6

    2 1 3

    5 4 6 2

    0

    0

    Sample Output

    1

    2

    Hint

    You need to determine the end of one line.In order to make it's easy to determine,there are no extra blank before the end of each line.

    Source

    Central Europe 1996

    #include<iostream>
    #include<cstdio>
    #include<cstring>
    using namespace std;
    #define N 105
    using namespace std;
    struct node {
    	int v,w,next;
    } edge[N*N];
    int dfn[N],low[N],vis[N],count[N],head[N];
    int n,m,num;
    void addedge(int u,int v) {
    	edge[num].v=v;
    	edge[num].next=head[u];
    	head[u]=num++;
    }
    void tarjan(int i) {
    	int j,k;
    	low[i]=dfn[i]=m++;
    	vis[i]=1;
    	for(j=head[i]; j!=-1; j=edge[j].next) {
    		k=edge[j].v;
    		if(!vis[k]) {
    			tarjan(k);
    			low[i]=min(low[k],low[i]);
    			if(low[k]>=dfn[i])
    				count[i]++;
    		} else
    			low[i]=min(low[i],dfn[k]);
    	}
    }
    int trans(char *s) {
    	int i,j;
    	i=j=0;
    	while(s[j]) {
    		i=i*10+s[j]-'0';
    		j++;
    	}
    	return i;
    }
    int main() {
    	char st[10],ch;
    	int i,j,ans;
    	while(1) {
    		scanf("%d",&n);
    		memset(head,-1,sizeof(head));
    		memset(count,0,sizeof(count));
    		memset(vis,0,sizeof(vis));
    		m=num=ans=0;
    		if(n==0)
    			break;
    		getchar();
    		while(1) {
    			scanf("%s",st);
    			if(st[0]=='0')
    				break;
    			i=trans(st);
    			while(1) {
    				ch=getchar();
    				if(ch=='
    ')
    					break;
    				scanf("%s",st);
    				j=trans(st);
    				addedge(i,j);
    				addedge(j,i);
    			}
    		}
    		tarjan(1);
    		for(i=2; i<=n; i++)
    			if(count[i])
    				ans++;
    		if(count[1]>1)
    			ans++;
    		printf("%d
    ",ans);
    	}
    	return 0;
    }
    

    思路:就是求割点的个数,还有就是读入的各种处理很麻烦。

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  • 原文地址:https://www.cnblogs.com/suishiguang/p/6391172.html
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