poj1144Network(无向图割点数)

题目请戳这里

题目大意：给一张无向图，求割点数量。

题目分析：tarjan算法求割点。关于无向图割点，这里说的很清楚了。直接建图跑一遍tarjan算法即可。

详情请见代码：

 

#include <iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int N = 101;
int adj[N][N];
bool flag[N][N],vis[N];
int low[N],dfn[N],subnets[N];
int n,dfns;
char s[N];

void dfs(int cur)
{
    int i;
    vis[cur] = true;
    dfn[cur] = low[cur] = dfns ++;
    for(i = 1;i <= adj[cur][0];i ++)
    {
        if(vis[adj[cur][i]] == false)
        {
            dfs(adj[cur][i]);
            low[cur] = min(low[cur],low[adj[cur][i]]);
            if(low[adj[cur][i]] >= dfn[cur])
                subnets[cur] ++;
        }
        else
            low[cur] = min(low[cur],dfn[adj[cur][i]]);
    }
}

void tarjan()
{
    int i;
    memset(vis,false,sizeof(vis));
    memset(subnets,0,sizeof(subnets));
    dfns = 1;
    for(i = 1;i <= n;i ++)
        if(vis[i] == false)
        {
            subnets[i] --;
            dfs(i);
        }
    int ans = 0;
    for(i = 1;i <= n;i ++)
        if(subnets[i] > 0)
            ans ++;
    printf("%d\n",ans);
}

int main()
{
    int i,j,p;
    freopen("in.txt","r",stdin);
    while(scanf("%d",&n),n)
    {
        memset(flag,false,sizeof(flag));
        memset(adj,0,sizeof(adj));
        while(scanf("%d",&i),i)
        {
            gets(s);
            p = 0;
            while(s[p] && s[p] == ' ')
                p ++;
            while(sscanf(s + p,"%d",&j) == 1)
            {
                if(flag[i][j] == false)
                {
                    flag[i][j] = flag[j][i] = true;
                    adj[i][++ adj[i][0]] = j;
                    adj[j][++ adj[j][0]] = i;
                }
                while(s[p] && s[p] != ' ')
                    p ++;
                while(s[p] && s[p] == ' ')
                    p ++;
            }
        }
        tarjan();
    }
    return 0;
}
//188K	16MS