Enumerate triangles
(Mylib/Graph/enumerate_triangles.cpp)
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Code
#pragma once
#include <tuple>
#include <unordered_set>
#include <vector>
#include "Mylib/Graph/Template/graph.cpp"
namespace haar_lib {
template <typename T>
std::vector<std::tuple<int, int, int>> enumerate_triangles(const graph<T> &g) {
const int N = g.size();
std::vector<std::tuple<int, int, int>> ret;
std::vector<std::unordered_set<int>> adjacent(N);
for (int i = 0; i < N; ++i) {
for (auto &e : g[i]) {
if (g[e.from].size() < g[e.to].size()) {
adjacent[e.from].insert(e.to);
} else if (g[e.from].size() == g[e.to].size()) {
if (e.from < e.to) {
adjacent[e.from].insert(e.to);
}
}
}
}
for (int i = 0; i < N; ++i) {
for (int j : adjacent[i]) {
for (int k : adjacent[j]) {
if (adjacent[i].find(k) != adjacent[i].end()) {
ret.emplace_back(i, j, k);
}
}
}
}
return ret;
}
} // namespace haar_lib
#line 2 "Mylib/Graph/enumerate_triangles.cpp"
#include <tuple>
#include <unordered_set>
#include <vector>
#line 2 "Mylib/Graph/Template/graph.cpp"
#include <iostream>
#line 4 "Mylib/Graph/Template/graph.cpp"
namespace haar_lib {
template <typename T>
struct edge {
int from, to;
T cost;
int index = -1;
edge() {}
edge(int from, int to, T cost) : from(from), to(to), cost(cost) {}
edge(int from, int to, T cost, int index) : from(from), to(to), cost(cost), index(index) {}
};
template <typename T>
struct graph {
using weight_type = T;
using edge_type = edge<T>;
std::vector<std::vector<edge<T>>> data;
auto& operator[](size_t i) { return data[i]; }
const auto& operator[](size_t i) const { return data[i]; }
auto begin() const { return data.begin(); }
auto end() const { return data.end(); }
graph() {}
graph(int N) : data(N) {}
bool empty() const { return data.empty(); }
int size() const { return data.size(); }
void add_edge(int i, int j, T w, int index = -1) {
data[i].emplace_back(i, j, w, index);
}
void add_undirected(int i, int j, T w, int index = -1) {
add_edge(i, j, w, index);
add_edge(j, i, w, index);
}
template <size_t I, bool DIRECTED = true, bool WEIGHTED = true>
void read(int M) {
for (int i = 0; i < M; ++i) {
int u, v;
std::cin >> u >> v;
u -= I;
v -= I;
T w = 1;
if (WEIGHTED) std::cin >> w;
if (DIRECTED)
add_edge(u, v, w, i);
else
add_undirected(u, v, w, i);
}
}
};
template <typename T>
using tree = graph<T>;
} // namespace haar_lib
#line 6 "Mylib/Graph/enumerate_triangles.cpp"
namespace haar_lib {
template <typename T>
std::vector<std::tuple<int, int, int>> enumerate_triangles(const graph<T> &g) {
const int N = g.size();
std::vector<std::tuple<int, int, int>> ret;
std::vector<std::unordered_set<int>> adjacent(N);
for (int i = 0; i < N; ++i) {
for (auto &e : g[i]) {
if (g[e.from].size() < g[e.to].size()) {
adjacent[e.from].insert(e.to);
} else if (g[e.from].size() == g[e.to].size()) {
if (e.from < e.to) {
adjacent[e.from].insert(e.to);
}
}
}
}
for (int i = 0; i < N; ++i) {
for (int j : adjacent[i]) {
for (int k : adjacent[j]) {
if (adjacent[i].find(k) != adjacent[i].end()) {
ret.emplace_back(i, j, k);
}
}
}
}
return ret;
}
} // namespace haar_lib
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