POJ 3694 Network

 

大意：让你求无向图的桥（割边）

思路：一次查询，重建一次图，然后求一次割边，TLE。去网上开了看资料，可以用LCA暴力查询，唔，改天看看LCA。

TLE CODE：

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

#define MAXN 100010
#define MAXM 500010

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

int first[MAXN], low[MAXN], dfn[MAXN];

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

void init1()
{
    cnt = 0;
    for(int i = 1; i <= n; i++) first[i] = -1;
}

void init2()
{
    scnt = top = tot = nbridge = 0;
    for(int i = 1; i <= n; i++) dfn[i] = 0;
}

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

void Tarjan(int u, int fa)
{
    int v;
    low[u] = dfn[u] = ++tot;
    bool repeat = 0;
    for(int e = first[u]; e != -1; e = edge[e].next)
    {
        v = edge[e].v;
        if(v == fa && !repeat)
        {
            repeat = 1;
            continue;
        }
        if(!dfn[v])
        {
            Tarjan(v, u);
            low[u] = min(low[u], low[v]);
            if(dfn[u] < low[v]) nbridge++;
        }
        low[u] = min(low[u], dfn[v]);
    }
}

void solve()
{
    init2();
    Tarjan(1, -1);
    printf("%d\n", nbridge);
}

int main()
{
    int times = 0;
    while(scanf("%d%d", &n, &m) && (n || m))
    {
        init1();
        while(m--)
        {
            int u, v;
            scanf("%d%d", &u, &v);
            read_graph(u, v);
            read_graph(v, u);
        }
        int Q;
        scanf("%d", &Q);
        printf("Case %d:\n", ++times);
        while(Q--)
        {
            int u, v;
            scanf("%d%d", &u, &v);
            read_graph(u, v);
            read_graph(v, u);
            solve();
        }
        printf("\n");
    }
    return 0;
}