bzoj1179 [Apio2009]Atm

Description

n,m⩽500000。

Solution

直接在原图上SPFA跑最长路肯定要GG（因为有环）。tarjan缩点后再跑SPFA就没事了。

#include<bits/stdc++.h>using namespace std;inline int read() {    int x = 0, flag = 1; char ch = getchar();    while (ch > '9' || ch < '0') { if (ch == '-') flag = -1; ch = getchar(); }    while (ch <= '9' && ch >= '0') { x = x * 10 + ch - '0'; ch = getchar(); }    return x * flag;}#define N 500001#define rep(ii, aa, bb) for (int ii = aa; ii <= bb; ii++)#define fech(i, x) for (int i = 0; i < x.size(); i++)#define INF 0x7fffffffint n, m;vector<int> g[N];struct edge { int u, v; }e[N];int mny[N];bool isBar[N];int ind, low[N], dfn[N];stack<int> stk;bool inStk[N];int belong[N];int scc;vector<int> sccHave[N];vector<int> sccG[N];int sccMny[N];int dis[N];void tarjan(int u) {    dfn[u] = low[u] = ++ind;    stk.push(u);    inStk[u] = 1;    fech(i, g[u]) {        int v = g[u][i];        if (!dfn[v]) tarjan(v), low[u] = min(low[u], low[v]);        else if (inStk[v]) low[u] = min(low[u], dfn[v]);    }    if (dfn[u] == low[u]) {        scc++;        int v;        do {            v = stk.top(); stk.pop(); inStk[v] = 0;            belong[v] = scc; sccHave[scc].push_back(v); sccMny[scc] += mny[v];        } while (u != v);    }}queue<int> q;bool vis[N];void spfa(int S) {    rep(i, 1, scc) dis[i] = -INF;    dis[S] = sccMny[S], vis[S] = 1, q.push(S);    while (q.size()) {        int u = q.front(); q.pop(), vis[u] = 0;        fech(i, sccG[u]) {            int v = sccG[u][i];            if (dis[v] < dis[u] + sccMny[v]) {                dis[v] = dis[u] + sccMny[v];                if (!vis[v]) q.push(v), vis[v] = 1;            }        }    }}int main() {    n = read(); m = read();    rep(i, 1, m) { int u = read(), v = read(); g[u].push_back(v); e[i].u = u, e[i].v = v; }    rep(i, 1, n) mny[i] = read();    rep(i, 1, n) if (!dfn[i]) tarjan(i);    rep(i, 1, m) if (belong[e[i].u] != belong[e[i].v]) sccG[belong[e[i].u]].push_back(belong[e[i].v]);    spfa(belong[read()]);    int P = read(), ans = -INF;    while (P--) ans = max(ans, dis[belong[read()]]);    cout << ans;    return 0;}