maximum-weight-matching/cpp/run_matching.cpp

/*
 * Calculate maximum weighted matching of graphs in DIMACS format.
 */

#include <cstdlib>
#include <cassert>
#include <cerrno>
#include <cstring>
#include <fstream>
#include <iostream>
#include <string>
#include <sstream>
#include <utility>
#include <vector>

#include "mwmatching.hpp"


namespace {  // anonymous namespace

typedef long long IntWeight;
typedef double FloatWeight;


template <typename WeightType>
using WeightedEdgeList = std::vector<mwmatching::Edge<WeightType>>;

using EdgeList = std::vector<mwmatching::VertexPair>;


/*
 * Graph defined by a list of weighted edges.
 * Weights are either integers or floating point numbers.
 */
struct Graph
{
    bool is_int_weight;
    WeightedEdgeList<IntWeight> int_edges;
    WeightedEdgeList<FloatWeight> float_edges;
};


/*
 * Matching defined by a list of matched edges.
 * The weight of the matching is either an integer or floating point number.
 */
struct Matching
{
    bool is_int_weight;
    IntWeight int_weight;
    FloatWeight float_weight;
    EdgeList pairs;
};


/* Parse an integer edge weight. */
bool parse_int_weight(const std::string& s, long long& v)
{
    const char *p = s.c_str();
    char *q;
    errno = 0;
    v = std::strtoll(p, &q, 10);
    return (q != p && q[0] == '\0' && errno == 0);
}


/* Parse a floating point edge weight. */
bool parse_float_weight(const std::string& s, double& v)
{
    const char *p = s.c_str();
    char *q;
    errno = 0;
    v = std::strtod(p, &q);
    return (q != p && q[0] == '\0' && errno == 0);

}


/* Read a graph in DIMACS edge list format. */
int read_dimacs_graph(std::istream& input, Graph& graph)
{
    graph.is_int_weight = true;
    graph.int_edges.clear();
    graph.float_edges.clear();

    while (!input.eof()) {
        std::string line;
        std::getline(input, line);
        if (!input) {
            if (input.eof()) {
                break;
            } else {
                return -1;
            }
        }

        line.erase(0, line.find_first_not_of(" \n\r\t"));
        line.erase(line.find_last_not_of(" \n\r\t") + 1);

        if (line.empty()) {
            // skip empty line
        } else if (line[0] == 'c') {
            // skip comment line
        } else if (line[0] == 'p') {
            // handle problem line
            std::istringstream is(line);
            std::string cmd, fmt;
            is >> cmd >> fmt;
            if (!is || cmd != "p" || fmt != "edge") {
                std::cerr << "ERROR: Expected DIMACS edge format but got '"
                          << line << "'" << std::endl;
                return -1;
            }
        } else if (line[0] == 'e') {
            // handle edge
            std::istringstream is(line);

            std::string cmd, weight;
            unsigned int x, y;
            IntWeight wi;
            FloatWeight wf;

            is >> cmd >> x >> y >> weight;
            if (!is || cmd != "e" || x < 1 || y < 1) {
                std::cerr << "ERROR: Expected edge but got '"
                          << line << "'" << std::endl;
                return -1;
            }

            if (graph.is_int_weight && parse_int_weight(weight, wi)) {
                wf = wi;
                graph.int_edges.emplace_back(x, y, wi);
            } else {
                if (!parse_float_weight(weight, wf)) {
                    std::cerr << "ERROR: Expected edge but got '"
                              << line << "'" << std::endl;
                    return -1;
                }
                graph.is_int_weight = false;
            }
            graph.float_edges.emplace_back(x, y, wf);

        } else {
            std::cerr << "ERROR: Unknown line format '" << line << "'"
                      << std::endl;
            return -1;
        }
    }

    if (graph.is_int_weight) {
        graph.float_edges.clear();
    } else {
        graph.int_edges.clear();
    }

    return 0;
}


/* Write matching in DIMACS format. */
void write_dimacs_matching(std::ostream& f, const Matching& matching)
{
    f << "s ";
    if (matching.is_int_weight) {
        f << matching.int_weight;
    } else {
        f.precision(12);
        f << matching.float_weight;
    }
    f << std::endl;
    for (auto pair : matching.pairs) {
        f << "m " << pair.first << " " << pair.second << std::endl;
    }
}


/* Solve a maximum-weight matching problem. */
template <typename WeightType>
EdgeList run_matching(const WeightedEdgeList<WeightType>& edges, bool maxcard)
{
    if (maxcard) {
        return mwmatching::maximum_weight_matching(
            mwmatching::adjust_weights_for_maximum_cardinality_matching(edges));
    } else {
        return mwmatching::maximum_weight_matching(edges);
    }
}


/* Calculate the total weight of the matched edges. */
template <typename WeightType>
WeightType matching_weight(const WeightedEdgeList<WeightType>& edges,
                           const EdgeList& pairs)
{
    unsigned int num_vertex = 0;
    for (const mwmatching::Edge<WeightType>& edge : edges) {
        if (edge.vt.first >= num_vertex) {
            num_vertex = edge.vt.first + 1;
        }
        if (edge.vt.second >= num_vertex) {
            num_vertex = edge.vt.second + 1;
        }
    }

    std::vector<mwmatching::VertexId> mate(num_vertex);
    for (const mwmatching::VertexPair& pair : pairs) {
        assert(mate[pair.first] == 0);
        assert(mate[pair.second] == 0);
        mate[pair.first] = pair.second;
        mate[pair.second] = pair.first;
    }

    WeightType weight = 0;
    for (const mwmatching::Edge<WeightType>& edge : edges) {
        if (mate[edge.vt.first] == edge.vt.second) {
            weight += edge.weight;
        }
    }

    return weight;
}


void usage()
{
    std::cerr
        << std::endl
        << "Calculate maximum weighted matching of a graph in DIMACS format."
        << std::endl << std::endl
        << "Usage: run_matching [--maxcard] < inputfile.edge" << std::endl
        << "   or: run_matching [--maxcard] inputfile.edge" << std::endl
        << std::endl
        << "    --maxcard       Calculate a maximum cardinality matching"
        << std::endl
        << "    inputfile.edge  Input file in DIMACS edge-list format"
        << std::endl << std::endl;
}

};  // anonymous namespace


int main(int argc, const char **argv)
{
    std::string input_file;
    bool maxcard = false;
    bool end_options = false;

    for (int i = 1; i < argc; i++) {
        if (!end_options && argv[i][0] == '-') {
            if (std::string("--help") == argv[i]
                    || std::string("-h") == argv[i]) {
                usage();
                return 0;
            } else if (std::string("--maxcard") == argv[i]) {
                maxcard = true;
            } else if (std::string("--") == argv[i]) {
                end_options = true;
            } else {
                std::cerr << "ERROR: Unknown option " << argv[i] << std::endl;
                usage();
                return 1;
            }
        } else {
            if (!input_file.empty()) {
                std::cerr << "ERROR: Multiple input files not supported."
                          << std::endl;
                usage();
                return 1;
            }
            input_file = argv[i];
        }
    }

    Graph graph;

    if (input_file.empty()) {
        if (read_dimacs_graph(std::cin, graph) != 0) {
            if (!std::cin) {
                std::cerr << "ERROR: Can not read from stdin ("
                          << std::strerror(errno) << ")" << std::endl;
            }
            return 1;
        }
    } else {
        std::ifstream f(input_file);
        if (!f) {
            std::cerr << "ERROR: Can not open '" << input_file << "' ("
                      << std::strerror(errno) << ")" << std::endl;
            return 1;
        }
        if (read_dimacs_graph(f, graph) != 0) {
            if (!f) {
                std::cerr << "ERROR: Can not read from '" << input_file
                          << "' (" << std::strerror(errno) << ")" << std::endl;
            }
            return 1;
        }
   }

    Matching matching;
    matching.is_int_weight = graph.is_int_weight;
    if (graph.is_int_weight) {
        matching.pairs = run_matching(graph.int_edges, maxcard);
        matching.int_weight = matching_weight(graph.int_edges,
                                              matching.pairs);
    } else {
        matching.pairs = run_matching(graph.float_edges, maxcard);
        matching.float_weight = matching_weight(graph.float_edges,
                                                matching.pairs);
    }

    write_dimacs_matching(std::cout, matching);

    return 0;
}