【模板】Tarjan 缩点 + 最长路

#include
#include
#include
#include
#include
#define maxn 101000
using namespace std;
typedef long long ll;
stack  S;
queue  Q;
ll w[maxn],scc[maxn],scc_cnt;
ll fst1[maxn],fst2[maxn],nxt1[maxn],nxt2[maxn];
ll tot1,tot2,ans;
ll dis[maxn],dis1[maxn];
ll ru[maxn],dfn[maxn],low[maxn],cnt;
bool vis[maxn];
struct edge{ll from,to;}es1[maxn<<2],es2[maxn<<1];
void build1(ll ff,ll tt)
{
    es1[++tot1] = (edge){ff,tt};
    nxt1[tot1] = fst1[ff];
    fst1[ff] = tot1;
}
void build2(ll ff,ll tt)
{
    es2[++tot2] = (edge){ff,tt};
    nxt2[tot2] = fst2[ff];
    fst2[ff] = tot2;
}
void tarjan(ll u)
{
    S.push(u);
    dfn[u] = low[u] = ++cnt;
    for(ll i = fst1[u];i;i = nxt1[i])
    {
        ll v = es1[i].to;
        if(!dfn[v])
        {
            tarjan(v);
            low[u] = min(low[u],low[v]);
        }
        else if(!scc[v])
        low[u] = min(low[u],dfn[v]);
    }
    if(dfn[u] == low[u])
    {
        scc_cnt ++;
        while(true)
        {
            ll t = S.top();
            S.pop();
            scc[t] = scc_cnt;
            dis[scc_cnt] += w[t];
            if(t == u) break;
        }
    }
}
void spfa(ll s)
{
    memset(dis1,0,sizeof(dis1));
    ans = max(ans,dis[s]);
    dis1[s]=dis[s]; 
    Q.push(s);
    vis[s] = 1;
    while(!Q.empty())
    {
        ll u = Q.front();
        Q.pop();
        vis[u] = 0;
        for(ll i = fst2[u];i;i = nxt2[i])
        {
            ll v = es2[i].to;
            if(dis1[u] + dis[v] > dis1[v])
            {
                dis1[v] = dis1[u]+dis[v];
                ans = max(ans,dis1[v]);
                if(!vis[v])
                {
                    Q.push(v); 
                    vis[v] = 1; 
                }
            }
        }
    }
}
int main()
{
    ll n,m;
    scanf("%lld%lld",&n,&m);
    for(ll i = 1;i <= n;i ++) scanf("%lld",&w[i]);
    for(ll i = 1;i <= m;i ++)
    {
        ll ff,tt;
        scanf("%lld%lld",&ff,&tt);
        build1(ff,tt);
    }
    for(ll i = 1;i <= n;i ++) if(!dfn[i]) tarjan(i);
    cout<for(int i=1;i<=scc_cnt;i++) cout<" scc "<for(ll i = 1;i <= tot1;i ++)
    {
        ll ff = es1[i].from;
        ll tt = es1[i].to;
        if(scc[ff] != scc[tt])
        {
            build2(scc[ff],scc[tt]);
            cout<"->"<for(int i=1;i<=scc_cnt;i++) build2(0,i);
    spfa(0);
    printf("%lld",ans);
    return 0;
}

最短路同理 处理Spfa即可