Topological Sort (トポロジカルソート)
(graph/topological_sort.hpp)

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• Last update: 2024-01-25 10:46:02+09:00
• Include: #include "graph/topological_sort.hpp"

• トポロジカルソートできない場合、空の配列を返す

Depends on

• graph/graph_template.hpp

Code

#pragma once

#include "graph/graph_template.hpp"
template <class T> std::vector<int> topological_sort(Graph<T> &G) {
    int N = (int)G.size();
    std::vector<int> indeg(N, 0);
    for (int i = 0; i < N; i++) {
        for (auto &e : G[i]) indeg[e.to]++;
    }
    std::vector<int> res;
    for (int i = 0; i < N; i++) {
        if (indeg[i] == 0) res.push_back(i);
    }
    int i = 0;
    while (i < (int)res.size()) {
        // determine whether topological sort is unique or not
        // or by checking the length of G's longest path is N - 1
        // if ((int)res.size() - i != 1) return std::vector<int>();
        int v = res[i];
        i++;
        for (auto &e : G[v]) {
            indeg[e.to]--;
            if (indeg[e.to] == 0) res.push_back(e.to);
        }
    }
    if ((int)res.size() != N) {
        return std::vector<int>();
    }
    return res;
}

#line 2 "graph/topological_sort.hpp"

#line 2 "graph/graph_template.hpp"

#include <vector>
template <class T> struct Edge {
    int from, to;
    T cost;
    int id;

    Edge() = default;
    Edge(int from, int to, T cost = 1, int id = -1) : from(from), to(to), cost(cost), id(id) {}

    friend std::ostream &operator<<(std::ostream &os, const Edge<T> &e) {
        // output format: "{ id : from -> to, cost }"
        return os << "{ " << e.id << " : " << e.from << " -> " << e.to << ", " << e.cost << " }";
    }
};

template <class T> using Edges = std::vector<Edge<T>>;
template <class T> using Graph = std::vector<std::vector<Edge<T>>>;
#line 4 "graph/topological_sort.hpp"
template <class T> std::vector<int> topological_sort(Graph<T> &G) {
    int N = (int)G.size();
    std::vector<int> indeg(N, 0);
    for (int i = 0; i < N; i++) {
        for (auto &e : G[i]) indeg[e.to]++;
    }
    std::vector<int> res;
    for (int i = 0; i < N; i++) {
        if (indeg[i] == 0) res.push_back(i);
    }
    int i = 0;
    while (i < (int)res.size()) {
        // determine whether topological sort is unique or not
        // or by checking the length of G's longest path is N - 1
        // if ((int)res.size() - i != 1) return std::vector<int>();
        int v = res[i];
        i++;
        for (auto &e : G[v]) {
            indeg[e.to]--;
            if (indeg[e.to] == 0) res.push_back(e.to);
        }
    }
    if ((int)res.size() != N) {
        return std::vector<int>();
    }
    return res;
}

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