mirror of
https://git.sb/baoshuo/OI-codes.git
synced 2024-12-25 18:12:04 +00:00
100 lines
1.9 KiB
C++
100 lines
1.9 KiB
C++
#include <iostream>
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#include <cstring>
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#include <queue>
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#include <stack>
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#include <vector>
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using std::cin;
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using std::cout;
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using std::endl;
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// Limits
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const int N = 10005;
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int n, m, u, v, a[N];
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std::vector<int> g[N], g2[N];
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// Tarjan
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int cnt, dfn[N], low[N];
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int scc_cnt, id[N];
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int w[N];
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bool vis[N];
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std::stack<int> st;
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void tarjan(int u) {
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dfn[u] = low[u] = ++cnt;
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vis[u] = true;
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st.push(u);
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for (int v : g[u]) {
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if (!dfn[v]) {
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tarjan(v);
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low[u] = std::min(low[u], low[v]);
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} else if (vis[v]) {
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low[u] = std::min(low[u], dfn[v]);
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}
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}
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if (low[u] == dfn[u]) {
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scc_cnt++;
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int v;
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do {
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v = st.top();
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st.pop();
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vis[v] = false;
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id[v] = scc_cnt;
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w[scc_cnt] += a[v];
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} while (v != u);
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}
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}
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// Shortest Path
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int dist[N];
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int spfa(int s) {
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memset(dist, -0x3f, sizeof(dist));
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std::queue<int> q;
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q.push(s);
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dist[s] = 0;
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int res = 0;
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while (!q.empty()) {
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int u = q.front();
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q.pop();
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res = std::max(res, dist[u] + w[u]);
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for (int v : g2[u]) {
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if (dist[v] < dist[u] + w[u]) {
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dist[v] = dist[u] + w[u];
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q.push(v);
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}
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}
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}
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return res;
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}
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int main() {
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cin >> n >> m;
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for (int i = 1; i <= n; i++) {
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cin >> a[i];
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}
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for (int i = 1; i <= m; i++) {
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cin >> u >> v;
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g[u].push_back(v);
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}
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for (int i = 1; i <= n; i++) {
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if (!dfn[i]) {
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tarjan(i);
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}
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}
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for (int i = 1; i <= n; i++) {
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for (int v : g[i]) {
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if (id[i] != id[v]) {
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g2[id[i]].push_back(id[v]);
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}
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}
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}
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int ans = 0;
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for (int i = 1; i <= scc_cnt; i++) {
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ans = std::max(ans, spfa(i));
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}
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cout << ans << endl;
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return 0;
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}
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