三角形列挙
(graph/enumerate_triangles.hpp)

• View this file on GitHub
• Last update: 2022-07-20 01:45:17+09:00
• Include: #include "graph/enumerate_triangles.hpp"

Verified with

• test/library_checker/graph/enumerate_triangles.test.cpp

Code

#pragma once
/**
 * @brief 三角形列挙
*/
vector<tuple<int, int, int>> enumerate_triangles(vector<vector<int>> &E){
  int N = E.size();
  vector<int> d(N);
  for (int i = 0; i < N; i++){
    d[i] = E[i].size();
  }
  vector<vector<int>> E2(N);
  for (int i = 0; i < N; i++){
    for (int j : E[i]){
      if (d[i] < d[j] || d[i] == d[j] && i < j){
        E2[i].push_back(j);
      }
    }
  }
  vector<bool> flg(N, false);
  vector<tuple<int, int, int>> ans;
  for (int i = 0; i < N; i++){
    for (int j : E2[i]){
      for (int k : E2[i]){
        flg[k] = true;
      }
      for (int k : E2[j]){
        if (flg[k]){
          ans.push_back(make_tuple(i, j, k));
        }
      }
      for (int k : E2[i]){
        flg[k] = false;
      }
    }
  }
  return ans;
}

#line 2 "graph/enumerate_triangles.hpp"
/**
 * @brief 三角形列挙
*/
vector<tuple<int, int, int>> enumerate_triangles(vector<vector<int>> &E){
  int N = E.size();
  vector<int> d(N);
  for (int i = 0; i < N; i++){
    d[i] = E[i].size();
  }
  vector<vector<int>> E2(N);
  for (int i = 0; i < N; i++){
    for (int j : E[i]){
      if (d[i] < d[j] || d[i] == d[j] && i < j){
        E2[i].push_back(j);
      }
    }
  }
  vector<bool> flg(N, false);
  vector<tuple<int, int, int>> ans;
  for (int i = 0; i < N; i++){
    for (int j : E2[i]){
      for (int k : E2[i]){
        flg[k] = true;
      }
      for (int k : E2[j]){
        if (flg[k]){
          ans.push_back(make_tuple(i, j, k));
        }
      }
      for (int k : E2[i]){
        flg[k] = false;
      }
    }
  }
  return ans;
}

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