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Commit 238082e

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4 files changed

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4 files changed

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‎graph_algorithms/course-schedule.cpp‎

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#include <bits/stdc++.h>
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using namespace std;
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typedef long long int lli;
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typedef vector<lli> vi;
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class Graph
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{
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lli nodes;
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vector<vi> adj;
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stack<lli> order;
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vector<bool> white;
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vector<bool> gray;
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vector<bool> black;
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public:
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Graph(lli _nodes)
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{
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this->nodes = _nodes;
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this->adj.resize(_nodes, vi{});
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this->white.resize(_nodes, true);
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this->gray.resize(_nodes, false);
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this->black.resize(_nodes, false);
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}
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void addEdge(lli src, lli dst)
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{
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this->adj[src - 1].emplace_back(dst - 1);
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}
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bool dfs(lli node)
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{
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this->white[node] = false;
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this->gray[node] = true;
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for (auto nxt : this->adj[node])
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{
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if(this->white[nxt]) {
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if(this->dfs(nxt) == false) {
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return false;
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}
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} else if (this->black[nxt]) {
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continue;
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} else if(this->gray[nxt]) {
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return false;
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}
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}
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this->order.push(node);
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this->gray[node] = false;
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this->black[node] = true;
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return true;
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}
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void solve()
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{
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for (lli i = 0; i < this->nodes; i++)
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{
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if (this->white[i])
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{
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if(dfs(i) == false) {
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cout<<"IMPOSSIBLE\n";
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return;
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}
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}
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}
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while (!this->order.empty())
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{
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cout << this->order.top() + 1 << ' ';
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this->order.pop();
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}
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cout << '\n';
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}
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};
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void task()
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{
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lli lenCourses, lenPrereqs;
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cin >> lenCourses >> lenPrereqs;
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Graph g(lenCourses);
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lli pre, nxt;
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for (lli i = 0; i < lenPrereqs; i++)
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{
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cin >> pre >> nxt;
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g.addEdge(pre, nxt);
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}
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g.solve();
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}
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int main()
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{
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ios::sync_with_stdio(false);
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cin.tie(NULL);
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task();
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return 0;
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}
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#include <bits/stdc++.h>
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using namespace std;
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typedef long long int lli;
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typedef vector<lli> vi;
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class Graph
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{
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vector<vi> adj;
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vi distances;
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vi parents;
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lli nodes;
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vi longestPath;
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public:
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Graph(lli _nodes)
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{
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this->nodes = _nodes;
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this->adj.resize(_nodes, vi{});
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this->distances.resize(_nodes, INT_MAX);
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this->parents.resize(_nodes, -1);
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}
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void addEdge(lli src, lli dst)
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{
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src--;
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dst--;
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if (find(this->adj[src].begin(), this->adj[src].end(), dst) == this->adj[src].end())
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{
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this->adj[src].emplace_back(dst);
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}
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}
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void dfs(lli node, lli parent, lli cost)
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{
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if (distances[node] > cost)
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{
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distances[node] = cost;
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parents[node] = parent;
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}
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for (auto nxt : this->adj[node])
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{
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this->dfs(nxt, node, cost - 1);
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}
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}
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void solve()
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{
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this->distances[0] = 0;
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this->dfs(0, -1, 0);
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if (this->distances[this->nodes - 1] == INT_MAX)
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{
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cout << "IMPOSSIBLE\n";
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return;
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}
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lli x = this->nodes - 1;
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stack<lli> path;
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cout << this->distances[this->nodes - 1] * -1 + 1 << '\n';
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while (x > -1)
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{
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path.push(x);
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x = parents[x];
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}
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while (!path.empty())
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{
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cout << path.top() + 1 << ' ';
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path.pop();
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}
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cout << '\n';
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}
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};
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void task()
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{
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lli lenCities, lenFlights;
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cin >> lenCities >> lenFlights;
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Graph g(lenCities);
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lli a, b;
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for (lli i = 0; i < lenFlights; i++)
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{
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cin >> a >> b;
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g.addEdge(a, b);
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}
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g.solve();
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}
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int main()
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{
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ios::sync_with_stdio(false);
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cin.tie(NULL);
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task();
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return 0;
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}

‎graph_algorithms/round-trip-ii.cpp‎

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#include <bits/stdc++.h>
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using namespace std;
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typedef long long int lli;
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typedef vector<lli> vi;
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typedef tuple<lli, lli> ii;
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typedef tuple<lli, lli, lli> iii;
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class Graph
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{
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vector<vi> adj;
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vector<bool> white;
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vector<bool> gray;
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vector<bool> black;
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vi parents;
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lli nodes;
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public:
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Graph(lli _nodes)
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{
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this->nodes = _nodes;
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this->adj.resize(this->nodes, vi{});
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this->white.resize(this->nodes, true);
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this->gray.resize(this->nodes, false);
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this->black.resize(this->nodes, false);
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this->parents.resize(this->nodes, -1);
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}
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bool isAvailable(lli src)
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{
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return this->white[src];
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}
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void addEdge(lli src, lli dst)
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{
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this->adj[src - 1].emplace_back(dst - 1);
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}
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bool dfs(lli node, lli parent)
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{
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this->white[node] = false;
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this->gray[node] = true;
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this->parents[node] = parent;
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for (auto nxt : this->adj[node])
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{
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if (this->black[nxt])
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{
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continue;
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}
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else if (this->white[nxt])
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{
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if (this->dfs(nxt, node))
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{
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return true;
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}
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}
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else if (this->gray[nxt])
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{
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// cycle detected
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vi cycle;
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lli x = node;
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while (x != nxt)
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{
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cycle.push_back(x);
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x = this->parents[x];
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}
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if (cycle.size() == 0)
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{
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continue;
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}
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cycle.push_back(nxt);
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cycle.push_back(node);
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reverse(cycle.begin(), cycle.end());
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cout << cycle.size() << '\n';
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for (auto n : cycle)
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{
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cout << n + 1 << ' ';
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}
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cout << '\n';
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return true;
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}
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}
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this->gray[node] = false;
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this->black[node] = true;
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return false;
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}
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};
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void task()
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{
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lli lenCities, lenFlights;
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cin >> lenCities >> lenFlights;
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Graph g(lenCities);
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lli a, b;
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for (lli i = 0; i < lenFlights; i++)
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{
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cin >> a >> b;
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g.addEdge(a, b);
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}
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for (lli i = 0; i < lenCities; i++)
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{
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if (g.isAvailable(i))
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{
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if (g.dfs(i, -1))
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{
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return;
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}
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}
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}
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cout<<"IMPOSSIBLE\n";
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}
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int main()
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{
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ios::sync_with_stdio(false);
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cin.tie(NULL);
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task();
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return 0;
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}

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