Caocao's Bridges HDU - 4738（Tarjan求割边模板题）

题目链接

题目意思:
求割边

#include 
#include 
#include 

using namespace std;

const int maxn = 1010;

int n, m, tot, num;
int head[maxn], dfn[maxn], low[maxn];
bool bridge[1000100 * 2];

struct node
{
    int v, w, next;
}edge[1000100 * 2];

inline void add(int u, int v, int w)
{
    edge[tot].v = v;
    edge[tot].w = w;
    edge[tot].next = head[u];
    head[u] = tot++;
}

inline void Init() {
    tot = 2;
    num = 0;
    memset(head, -1, sizeof(head));
    memset(dfn, -1, sizeof(dfn));
    memset(bridge, false, sizeof(bridge));
}

void Tarjan(int u, int edge_id)
{
    dfn[u] = low[u] = ++num;
    for(int i = head[u]; i != -1; i = edge[i].next)
    {
        int v = edge[i].v;
        if(dfn[v] == -1)
        {
            Tarjan(v, i);
            low[u] = min(low[u], low[v]);
            if(low[v] > dfn[u])
            {
                bridge[i] = true;
                bridge[i ^ 1] = true;
            }
        }
        else if(i != (edge_id^1))
        {
            low[u] = min(low[u], dfn[v]);
        }
    }
}

int main()
{
    //freopen("in.txt", "r", stdin);
    while(cin >> n >> m && n && m)
    {
        Init();
        int u, v, w;
        for(int i = 1; i <= m; ++ i)
        {
            scanf("%d%d%d", &u, &v, &w);
            add(u, v, w);
            add(v, u, w);
        }
        Tarjan(1, 0);
        bool flag = false;      //如果图本身就不是连通图，就没必要派人去炸桥了，答案直接就是０
        for(int i = 1; i <= n; ++ i) {
            if(dfn[i] == -1) {
                flag = true;
                break;
            }
        }
        if(flag) {
            cout << 0 << endl;
            continue;
        }
        //如果图是连通的
        int mins = 0x3f3f3f3f;
        for(int i = 2; i < tot; i += 2)
        {
            if(bridge[i])
            {
                mins = min(mins, edge[i].w);
            }
        }
        if(mins == 0x3f3f3f3f)
        {
            cout << -1 << endl;
        }
        else 
        {
            if(mins == 0)　　//还要看是不是守桥的人数为０，如果是这样的话，那也要派一个人去
                mins = 1;
            cout << mins << endl;
        }
    }
    return 0;
}