HDU 3394 Railway 双连通求块

大意略。

无向图求双连通块，冲突的边，即缩块之后如果点数>边数，说明无环，则该路径可以去掉。如果有环，则环中所有的边都冲突。

 

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <string>
#include <cstring>
#include <cmath>
#include <vector>
#include <queue>
#include <algorithm>
#include <map>
using namespace std;

const int maxn = 10010;
const int maxm = 100010*2;

struct Edge
{
    int v, w;
    int next;
    int id;
}edge[maxm];

int first[maxn], stack[maxn], ins[maxn], dfn[maxn], low[maxn];
int belong[maxn];
int deg[maxn];
int block[maxn];

int n, m;
int cnt;
int scnt, top, tot;

void init()
{
    cnt = 0;
    scnt = top = tot = 0;
    memset(first, -1, sizeof(first));
    memset(dfn, 0, sizeof(dfn));
    memset(ins, 0, sizeof(ins));
    memset(block, 0, sizeof(block));
}

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

bool vis[maxn];

int ans1, ans2;

void count_edge()
{
    memset(vis, 0, sizeof(vis));
    int sum = 0;
    for(int i = 1; i <= block[0]; i++) vis[block[i]] = 1;
    for(int i = 1; i <= block[0]; i++)
    {
        int u = block[i];
        for(int e = first[u]; e != -1; e = edge[e].next)
        {
            int v = edge[e].v;
            if(vis[v]) sum++;
        }
    }
    sum /= 2;
    if(sum < block[0]) ans1 += sum;
    if(sum > block[0]) ans2 += sum;
}

void dfs(int u)
{
    int v;
    low[u] = dfn[u] = ++tot;
    stack[top++] = u;
    ins[u] = 1;
    for(int e = first[u]; e != -1; e = edge[e].next)
    {
        v = edge[e].v;
        if(!dfn[v])
        {
            dfs(v);
            low[u] = min(low[u], low[v]);
            if(dfn[u] <= low[v])
            {
                block[0] = 0;
                int t;
                do
                {
                    t = stack[--top];
                    block[++block[0]] = t;
                    ins[t] = 0;
                }while(v != t);
                block[++block[0]] = u;
                count_edge();
            }
        }
        else if(ins[v]) low[u] = min(low[u], dfn[v]);
    }
}

void Tarjan()
{
    for(int i = 0; i < n; i++) if(!dfn[i]) dfs(i);
}

int read_case()
{
    init();
    scanf("%d%d", &n, &m);
    if(!n) return 0;
    while(m--)
    {
        int u, v, w;
        scanf("%d%d", &u, &v);
        read_graph(u, v);
        read_graph(v, u);
    }
    return 1;
}

void solve()
{
    ans1 = ans2 = 0;
    Tarjan();
    printf("%d %d\n", ans1, ans2);
}

int main()
{
    while(read_case())
    {
        solve();
    }
    return 0;
}