【POJ】2117 Electricity

无向图求割点和连通块。

/* POJ2117 */
#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cstdlib>
using namespace std;

#define MAXN 10005

vector<int> vc[MAXN];
int low[MAXN], pre[MAXN];
int n, m;
int dfs_clock, ans, link;

void init() {
    int i;
    
    for (i=0; i<n; ++i)
        vc[i].clear();
    
    memset(pre, 0, sizeof(int)*n);
    dfs_clock = ans = link = 0;
}

void tarjan(int u, int fa) {
    int i, j, k, v;
    int child = 0;
    int cnt = 0;
    
    pre[u] = low[u] = ++dfs_clock;
    for (i=0; i<vc[u].size(); ++i) {
        v = vc[u][i];
        if (!pre[v]) {
            ++child;
            tarjan(v, u);
            low[u] = min(low[u], low[v]);
            if (low[v] >= pre[u]) {
                ++cnt;
            }
        } else if (pre[v]<pre[u] && v!=fa){
            low[u] = min(low[u], pre[v]);
        }
    }
    if (fa == -1) {
        if (child > 1)
            ans = max(ans, child-1);
    } else {
        ans = max(ans, cnt);
    }
}

int main() {
    int i, j, k;
    
    #ifndef ONLINE_JUDGE
        freopen("data.in", "r", stdin);
        freopen("data.out", "w", stdout);
    #endif
    
    while (scanf("%d %d",&n,&m)!=EOF && (n||m)) {
        if (m == 0) {
            printf("%d
", n-1);
            continue;
        }
        init();
        for (i=0; i<m; ++i) {
            scanf("%d %d", &j, &k);
            vc[j].push_back(k);
            vc[k].push_back(j);
        }
        for (i=0; i<n; ++i) {
            if (!pre[i]) {
                ++link;
                tarjan(i, -1);
            }
        }
        printf("%d
", ans+link);
    }
    
    return 0;
}