This documentation is automatically generated by online-judge-tools/verification-helper
#include "graph/others/cycle-detection.hpp"
有向グラフが与えられたとき, 辺素なサイクルを $1$ つみつける.
適当な頂点から DFS すると見つけられる.
build()
: 辺素なサイクルを $1$ つ見つけて返す. ただし, 見つからなかったとき空列を返す.$O(E + V)$
#pragma once
#include "../graph-template.hpp"
/**
* @brief Cycle Detection(閉路検出)
*
*/
template< typename T = int >
struct CycleDetection : Graph< T > {
using Graph< T >::Graph;
using Graph< T >::g;
vector< int > used;
Edges< T > pre, cycle;
bool dfs(int idx) {
used[idx] = 1;
for(auto &e : g[idx]) {
if(used[e] == 0) {
pre[e] = e;
if(dfs(e)) return true;
} else if(used[e] == 1) {
int cur = idx;
while(cur != e) {
cycle.emplace_back(pre[cur]);
cur = pre[cur].from;
}
cycle.emplace_back(e);
return true;
}
}
used[idx] = 2;
return false;
}
Edges< T > build() {
used.assign(g.size(), 0);
pre.resize(g.size());
for(int i = 0; i < (int) g.size(); i++) {
if(used[i] == 0 && dfs(i)) {
reverse(begin(cycle), end(cycle));
return cycle;
}
}
return {};
}
};
#line 2 "graph/others/cycle-detection.hpp"
#line 2 "graph/graph-template.hpp"
/**
* @brief Graph Template(グラフテンプレート)
*/
template< typename T = int >
struct Edge {
int from, to;
T cost;
int idx;
Edge() = default;
Edge(int from, int to, T cost = 1, int idx = -1) : from(from), to(to), cost(cost), idx(idx) {}
operator int() const { return to; }
};
template< typename T = int >
struct Graph {
vector< vector< Edge< T > > > g;
int es;
Graph() = default;
explicit Graph(int n) : g(n), es(0) {}
size_t size() const {
return g.size();
}
void add_directed_edge(int from, int to, T cost = 1) {
g[from].emplace_back(from, to, cost, es++);
}
void add_edge(int from, int to, T cost = 1) {
g[from].emplace_back(from, to, cost, es);
g[to].emplace_back(to, from, cost, es++);
}
void read(int M, int padding = -1, bool weighted = false, bool directed = false) {
for(int i = 0; i < M; i++) {
int a, b;
cin >> a >> b;
a += padding;
b += padding;
T c = T(1);
if(weighted) cin >> c;
if(directed) add_directed_edge(a, b, c);
else add_edge(a, b, c);
}
}
inline vector< Edge< T > > &operator[](const int &k) {
return g[k];
}
inline const vector< Edge< T > > &operator[](const int &k) const {
return g[k];
}
};
template< typename T = int >
using Edges = vector< Edge< T > >;
#line 4 "graph/others/cycle-detection.hpp"
/**
* @brief Cycle Detection(閉路検出)
*
*/
template< typename T = int >
struct CycleDetection : Graph< T > {
using Graph< T >::Graph;
using Graph< T >::g;
vector< int > used;
Edges< T > pre, cycle;
bool dfs(int idx) {
used[idx] = 1;
for(auto &e : g[idx]) {
if(used[e] == 0) {
pre[e] = e;
if(dfs(e)) return true;
} else if(used[e] == 1) {
int cur = idx;
while(cur != e) {
cycle.emplace_back(pre[cur]);
cur = pre[cur].from;
}
cycle.emplace_back(e);
return true;
}
}
used[idx] = 2;
return false;
}
Edges< T > build() {
used.assign(g.size(), 0);
pre.resize(g.size());
for(int i = 0; i < (int) g.size(); i++) {
if(used[i] == 0 && dfs(i)) {
reverse(begin(cycle), end(cycle));
return cycle;
}
}
return {};
}
};