无向图连通分量

割顶：

　　POJ1144：求割顶的数量　

#include <iostream>
#include <string.h>
#include <cstdio>
#include <queue>
#include <math.h>
#include <cstring>
#include <algorithm>
#include <sstream>

#define SIGMA_SIZE 26
#pragma warning ( disable : 4996 )

using namespace std;
typedef long long LL;

inline LL LMax(LL a,LL b)    { return a>b?a:b; }
inline LL LMin(LL a,LL b)    { return a>b?b:a; }
inline int Max(int a,int b) { return a>b?a:b; }
inline int Min(int a,int b) { return a>b?b:a; }
inline int gcd( int a, int b ) { return b==0?a:gcd(b,a%b); }
inline int lcm( int a, int b ) { return a/gcd(a,b)*b; }  //a*b = gcd*lcm
const int inf  = 0x3f3f3f3f;
const int mod  = 7;
const int maxn = 105;
const int maxk = 200;


int N, dfs_clock;
vector<int> mmap[maxn];
int low[maxn<<1], pre[maxn<<1];
bool iscut[maxn];

int dfs( int x, int fa )
{
    int lowu = pre[x] = ++dfs_clock;
    int child = 0;

    for (int i = 0; i < mmap[x].size(); i++ )
    {
        int tmp = mmap[x][i];
        if ( !pre[tmp] )
        {
            child++;
            int lowv = dfs( tmp, x );
            lowu = Min(lowu, lowv);

            if ( lowv >= pre[x] )
                iscut[x] = true;
        } else if ( pre[tmp] < pre[x] && tmp != fa )
            lowu = Min(lowu, pre[tmp]);
    }

    if ( fa < 0 && child == 1 ) iscut[x] = 0;

    low[x] = lowu;
    return lowu;
}

void init()
{
    memset( mmap, 0, sizeof(mmap) );
    memset( pre, 0, sizeof(pre) );
    memset( iscut, 0, sizeof(iscut) ); 

    for( int i = 0; i < maxn; i++ )
        mmap[i].clear();
    dfs_clock = 0;
}

int main()
{
    int x, y;
    string str;
    stringstream ss;

    while ( getline(cin, str) )
    {
        init();
        ss.clear(); ss << str;
        ss >> N;
        if (!N) break;

        
        while ( getline(cin, str) )
        {

            ss.clear(); ss << str;
            ss >> x;

            if ( !x ) break;
            while ( ss >> y )
                { mmap[x].push_back(y); mmap[y].push_back(x); }
        }

        dfs(1,-1);

        int ans = 0;
        for( int i = 1; i <= N; i++ )
            if ( iscut[i] ) ans++;
        cout << ans << endl;
    }
    
    return 0;
}