POJ 1144 Network

 

无双图求割顶的个数，Tarjan模板。

我这里有两种模板，似乎第一种比较简单。

CODE1：

#include <iostream>
#include <cstdio>   
#include <cstring>
#include <cstdlib>
using namespace std;

#define MAXN 110
#define MAXM 10010

struct Edge
{  
    int v, next;  
}edge[MAXM]; 

 
int first[MAXN];
int dfn[MAXN], low[MAXN];
int sub[MAXN]; //保存的删除该节点之后，图分散变成子图的数量。 
  
int n;
int cnt, tot;
int u, v;

inline void init()
{
    cnt = 0;
    tot = 0;
    memset(first, -1, sizeof(first));
    memset(dfn, 0, sizeof(dfn));
    memset(sub, 0, sizeof(sub));
}

inline void read_graph(int u, int v)
{  
    edge[cnt].v = v;  
    edge[cnt].next = first[u], first[u] = cnt++;  
}  

inline void read_graph2()
{
    while(scanf("%d", &u) && u)
    {
        while(getchar() != '\n')
        {
            scanf("%d", &v);  
            read_graph(u, v);  
            read_graph(v, u);  
        }
    }
}

void Tarjan(int u) //不直接判断是否为根，而是将root的sub值赋值为0 
{
    dfn[u] = low[u] = ++tot;
    for(int e = first[u]; e != -1; e = edge[e].next)
    {
        int v = edge[e].v;
        if(!dfn[v])
        {
            Tarjan(v);
            low[u] = min(low[u], low[v]);
            if(dfn[u] <= low[v]) sub[u]++;
        }
        low[u] = min(low[u], dfn[v]);
    }
}

void solve(int root)
{
    int ans = 0;
    for(int i = 1; i <= n; i++) sub[i] = (i == root)? 0:1;
    Tarjan(root);
    for(int i = 1; i <= n; i++)
    {
        if(sub[i] > 1) ans++; //若大于1，则说明是割顶。 
    }
    printf("%d\n", ans);
}

int main()  
{  
    while(scanf("%d", &n) && n)
    {
        init();
        read_graph2();
        solve(1);
    }
    return 0;  
}  

 

CODE2：

#include <iostream>
#include <cstdio>   
#include <cstring>
#include <cstdlib>
using namespace std;
struct Edge
{  
    int v, next;  
}edge[10001]; 

 
int first[101];
int dfn[101], low[101];
int sub[101];
  
int n;
int cnt, tot, root = 1;
int u, v;

inline void init()
{
    cnt = 0;
    tot = 0;
    memset(first, -1, sizeof(first));
    memset(dfn, 0, sizeof(dfn));
}

inline void read_graph(int u, int v)
{  
    edge[cnt].v = v;  
    edge[cnt].next = first[u], first[u] = cnt++;  
}  

inline void read_graph2()
{
    while(scanf("%d", &u) && u)
    {
        while(getchar() != '\n')
        {
            scanf("%d", &v);  
            read_graph(u, v);  
            read_graph(v, u);
        }
    }
}

void Tarjan(int u, int fa) //处理的时候判断是否为根。
{
    int rootson = 0;
    low[u] = dfn[u] = ++tot;
    for(int e = first[u]; e != -1; e = edge[e].next)
    {
        int v = edge[e].v;
        if(!dfn[v])
        {
            if(u == root)
            {
                if(++rootson > 1) sub[u]++;
            }
            Tarjan(v, u);
            low[u] = min(low[u], low[v]);
            if(u != root && dfn[u] <= low[v]) sub[u]++;
        }
        low[u] = min(low[u], dfn[v]);
    }
}

void solve()
{
    int ans = 0;
    for(int i = 1; i <= n; i++) sub[i] = 1;
    Tarjan(root, -1);
    for(int i = 1; i <= n; i++)
    {
        if(sub[i] > 1) ans++;
    }
    printf("%d\n", ans);
}

int main()  
{  
    while(scanf("%d", &n) && n)
    {
        init();
        read_graph2();
        solve();
    }
    return 0;  
}