83 lines
2.2 KiB
C++
83 lines
2.2 KiB
C++
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#include <vector>
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#include <climits>
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#include <iostream>
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using namespace std;
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typedef pair<int, int> pii;
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typedef vector<vector<pii> > Graph;
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const int INF = INT_MAX / 3;
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bool bellmanFord(Graph &g, int s, vector<int> &prio, vector<int> &pred) {
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int n = g.size();
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pred.assign(n, -1);
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prio.assign(n, INF);
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prio[s] = 0;
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bool wasChanged = true;
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for (int k = 0; k < n; k++) {
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wasChanged = false;
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for (int u = 0; u < n; u++) {
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for (int i = 0; i < (int) g[u].size(); i++) {
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int v = g[u][i].first;
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int cost = g[u][i].second;
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if (prio[v] > prio[u] + cost) {
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prio[v] = prio[u] + cost;
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pred[v] = u;
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wasChanged = true;
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}
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}
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}
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if (!wasChanged)
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break;
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}
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// wasChanged is true iff graph has a negative cycle
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return wasChanged;
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}
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vector<int> findNegativeCycle(Graph &g) {
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int n = g.size();
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vector<int> pred(n, -1);
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vector<int> prio(n, INF);
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prio[0] = 0;
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int last = 0;
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for (int k = 0; k < n; k++) {
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last = -1;
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for (int u = 0; u < n; u++) {
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for (int i = 0; i < (int) g[u].size(); i++) {
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int v = g[u][i].first;
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int cost = g[u][i].second;
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if (prio[v] > prio[u] + cost) {
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prio[v] = prio[u] + cost;
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pred[v] = u;
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last = v;
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}
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}
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}
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if (last == -1)
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return vector<int>();
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}
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vector<int> path(n);
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vector<int> pos(n, -1);
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for (int i = 0;; i++) {
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if (pos[last] != -1)
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return vector<int>(path.rend() - i, path.rend() - pos[last]);
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path[i] = last;
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pos[last] = i;
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last = pred[last];
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}
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}
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int main() {
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Graph g(4);
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g[0].push_back(make_pair(1, 1));
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g[1].push_back(make_pair(0, 1));
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g[1].push_back(make_pair(2, 1));
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g[2].push_back(make_pair(3, -10));
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g[3].push_back(make_pair(1, 1));
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vector<int> cycle = findNegativeCycle(g);
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for (int i = 0; i < (int) cycle.size(); i++)
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cout << cycle[i] << " ";
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}
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