poj1144

求无向图的割顶和桥的裸题。

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int maxn = 105, maxm = maxn * maxn;

int n, m, tot, dfs_clock;

int h[maxn], dfn[maxn], low[maxn], iscut[maxn];
 
struct edge
{
    int v, next;
}a[maxm];

void add(int x, int y)
{
    a[tot].v = y;
    a[tot].next = h[x];
    h[x] = tot++;
}

int dfs(int u, int fa)
{
    int lowu = dfn[u] = ++dfs_clock;
    int child = 0;
    for (int i = h[u]; ~i; i = a[i].next)
    {
        int v = a[i].v;
        if (!dfn[v])
        {
            child++;
            int lowv = dfs(v, u);
            lowu = min(lowu, lowv);
            if (lowv >= dfn[u])
            {
                iscut[u] = 1;
            }
//            if (lowv > dfn[u])
//            {
//                printf("%d - %d\n", u, v);
//            }
        }else if (dfn[v] < dfn[u] && v != fa)
        {
            lowu = min(lowu, dfn[v]);
        }
    }
    if (fa == 0 && child == 1)
    {
        iscut[u] = 0;
    }
    low[u] = lowu;
    return lowu;
}

int main()
{
//    freopen("poj1144.in","r",stdin);
    while (scanf("%d", &n) && n)
    {
        memset(h, -1, sizeof h); tot = dfs_clock = 0;
        memset(low, 0, sizeof low);
        memset(dfn, 0, sizeof dfn);
        memset(iscut, 0, sizeof iscut);
        int x;
        while (scanf("%d", &x) && x)
        {
            while (getchar() != '\n')
            {
                int y;
                scanf("%d", &y);
                add(x, y); add(y, x);
            }
        }
        dfs(1, 0);
        int ans = 0;
        for (int i = 1; i <= n; i++)
            if (iscut[i])
                ans++;
        printf("%d\n", ans);
    }
    return 0;
}

恶心的地方在于读入，以及千万不要忘记初始化！！！