Add program for matching with LEMON
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1e81129476
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80dd53c736
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CXX = g++
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CXXFLAGS = -std=c++11 -Wall -O2
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LDLIBS = -llemon
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lemon_matching: lemon_matching.cc
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.PHONY: clean
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clean:
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$(RM) lemon_matching
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/*
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* Use LEMON to solve a maximum-weight matching problem.
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*
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* This program is designed for LEMON version 1.3.1.
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*
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* Download LEMON from https://lemon.cs.elte.hu/trac/lemon
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* or install Debian package "liblemon-dev".
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*
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* This program reads input from stdin or from a specified filename.
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* Input should be a weighted graph in DIMACS edge-list format.
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*
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* This program writes output to stdout.
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* The output is a matching in DIMACS matching format.
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*/
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#include <cstdlib>
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#include <cerrno>
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#include <cstring>
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#include <fstream>
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#include <iostream>
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#include <string>
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#include <sstream>
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#include <unordered_map>
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#include <utility>
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#include <lemon/smart_graph.h>
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#include <lemon/matching.h>
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namespace { // anonymous namespace
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typedef long long IntWeight;
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typedef double FloatWeight;
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/* Weighted edge. */
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template <typename WeightType>
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struct WeightedEdge
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{
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int x, y;
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WeightType w;
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WeightedEdge(int x, int y, WeightType w)
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: x(x), y(y), w(w)
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{ }
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};
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/* Graph defined by a list of weighted edges. */
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template <typename WeightType>
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using WeightedEdgeList = std::vector<WeightedEdge<WeightType>>;
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/* Wrapper that holds an edge list with either integer or float weights. */
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struct WeightedEdgeListVariant
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{
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bool is_int_weight;
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WeightedEdgeList<IntWeight> int_edges;
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WeightedEdgeList<FloatWeight> float_edges;
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};
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/* Matching defined by a list of matched edges. */
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struct Matching
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{
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bool is_int_weight;
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IntWeight int_weight;
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FloatWeight float_weight;
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std::vector<std::pair<int, int>> pairs;
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Matching() = default;
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Matching(IntWeight weight, std::vector<std::pair<int, int>>&& pairs)
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: is_int_weight(true),
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int_weight(weight),
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float_weight(0),
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pairs(pairs)
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{ }
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Matching(FloatWeight weight, std::vector<std::pair<int, int>>&& pairs)
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: is_int_weight(false),
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int_weight(0),
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float_weight(weight),
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pairs(pairs)
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{ }
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};
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/* Wrapper for a LEMON graph with edge weights and node indices. */
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template <typename WeightType>
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struct LemonGraph
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{
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lemon::SmartGraph graph;
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lemon::SmartGraph::NodeMap<int> node_index;
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lemon::SmartGraph::EdgeMap<WeightType> edge_weight;
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/* Construct a LEMON graph from a list of weighted edges. */
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explicit LemonGraph(const WeightedEdgeList<WeightType>& edges)
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: graph(),
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node_index(graph),
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edge_weight(graph)
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{
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std::unordered_map<int, lemon::SmartGraph::Node> node_map;
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for (const WeightedEdge<WeightType>& e : edges) {
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lemon::SmartGraph::Node node_x = node_from_index(node_map, e.x);
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lemon::SmartGraph::Node node_y = node_from_index(node_map, e.y);
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lemon::SmartGraph::Edge edge = graph.addEdge(node_x, node_y);
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edge_weight.set(edge, e.w);
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}
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}
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private:
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/* Return the Node that corresponds to the specified vertex index. */
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lemon::SmartGraph::Node
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node_from_index(std::unordered_map<int, lemon::SmartGraph::Node>& node_map,
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int x)
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{
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auto it = node_map.find(x);
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if (it == node_map.end()) {
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lemon::SmartGraph::Node node = graph.addNode();
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node_index.set(node, x);
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node_map[x] = node;
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return node;
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} else {
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return it->second;
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}
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}
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};
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/* Parse an integer edge weight. */
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bool parse_int_weight(const std::string& s, long long& v)
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{
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const char *p = s.c_str();
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char *q;
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errno = 0;
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v = std::strtoll(p, &q, 10);
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return (q != p && q[0] == '\0' && errno == 0);
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}
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/* Parse a floating point edge weight. */
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bool parse_float_weight(const std::string& s, double& v)
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{
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const char *p = s.c_str();
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char *q;
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errno = 0;
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v = std::strtod(p, &q);
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return (q != p && q[0] == '\0' && errno == 0);
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}
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/* Read a graph in DIMACS edge list format. */
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int read_dimacs_graph(std::istream& input, WeightedEdgeListVariant& res)
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{
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res.is_int_weight = true;
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res.int_edges.clear();
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res.float_edges.clear();
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while (!input.eof()) {
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std::string line;
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std::getline(input, line);
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if (!input) {
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if (input.eof()) {
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break;
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} else {
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return -1;
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}
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}
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line.erase(0, line.find_first_not_of(" \n\r\t"));
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line.erase(line.find_last_not_of(" \n\r\t") + 1);
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if (line.empty()) {
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// skip empty line
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} else if (line[0] == 'c') {
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// skip comment line
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} else if (line[0] == 'p') {
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// handle problem line
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std::istringstream is(line);
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std::string cmd, fmt;
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is >> cmd >> fmt;
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if (!is || cmd != "p" || fmt != "edge") {
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std::cerr << "ERROR: Expected DIMACS edge format but got '"
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<< line << "'" << std::endl;
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return -1;
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}
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} else if (line[0] == 'e') {
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// handle edge
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std::istringstream is(line);
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std::string cmd, weight;
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unsigned int x, y;
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IntWeight wi;
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FloatWeight wf;
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is >> cmd >> x >> y >> weight;
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if (!is || cmd != "e" || x < 1 || y < 1) {
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std::cerr << "ERROR: Expected edge but got '"
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<< line << "'" << std::endl;
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return -1;
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}
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if (res.is_int_weight && parse_int_weight(weight, wi)) {
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wf = wi;
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res.int_edges.push_back(WeightedEdge<IntWeight>(x, y, wi));
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} else {
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if (!parse_float_weight(weight, wf)) {
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std::cerr << "ERROR: Expected edge but got '"
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<< line << "'" << std::endl;
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return -1;
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}
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res.is_int_weight = false;
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}
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res.float_edges.push_back(WeightedEdge<FloatWeight>(x, y, wf));
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} else {
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std::cerr << "ERROR: Unknown line format '" << line << "'"
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<< std::endl;
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return -1;
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}
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}
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if (res.is_int_weight) {
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res.float_edges.clear();
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} else {
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res.int_edges.clear();
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}
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return 0;
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}
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/* Write matching in DIMACS format. */
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void write_dimacs_matching(std::ostream& f, const Matching& matching)
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{
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f << "s ";
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if (matching.is_int_weight) {
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f << matching.int_weight;
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} else {
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f.precision(12);
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f << matching.float_weight;
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}
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f << std::endl;
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for (auto pair : matching.pairs) {
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f << "m " << pair.first << " " << pair.second << std::endl;
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}
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}
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/* Solve a maximum-weight-matching problem. */
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template <typename WeightType>
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Matching run_matching(const WeightedEdgeList<WeightType>& edges)
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{
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LemonGraph<WeightType> lemon_graph(edges);
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lemon::MaxWeightedMatching<lemon::SmartGraph,
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lemon::SmartGraph::EdgeMap<WeightType>>
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match(lemon_graph.graph, lemon_graph.edge_weight);
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match.run();
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std::vector<std::pair<int, int>> pairs;
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for (lemon::SmartGraph::NodeIt node_x(lemon_graph.graph);
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node_x != lemon::INVALID;
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++node_x) {
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lemon::SmartGraph::Node node_y = match.mate(node_x);
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if (node_y != lemon::INVALID) {
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int x = lemon_graph.node_index[node_x];
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int y = lemon_graph.node_index[node_y];
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if (x < y) {
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pairs.push_back(std::make_pair(x, y));
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}
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}
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}
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return Matching(match.matchingWeight(), std::move(pairs));
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}
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void usage()
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{
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std::cerr
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<< std::endl
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<< "Solves a maximum-weight matching problem with LEMON."
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<< std::endl << std::endl
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<< "Usage: lemon_matching < inputfile.gr" << std::endl
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<< " or: lemon_matching inputfile.gr" << std::endl
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<< std::endl
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<< " inputfile.gr Input file in DIMACS edge-list format"
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<< std::endl << std::endl;
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}
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}; // anonymous namespace
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int main(int argc, const char **argv)
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{
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std::string input_file;
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bool end_options = false;
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for (int i = 1; i < argc; i++) {
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if (!end_options && argv[i][0] == '-') {
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if (std::string("--help") == argv[i]
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|| std::string("-h") == argv[i]) {
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usage();
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return 0;
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} else if (std::string("--") == argv[i]) {
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end_options = true;
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} else {
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std::cerr << "ERROR: Unknown option " << argv[i] << std::endl;
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usage();
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return 1;
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}
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} else {
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if (!input_file.empty()) {
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std::cerr << "ERROR: Multiple input files not supported."
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<< std::endl;
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usage();
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return 1;
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}
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input_file = argv[i];
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}
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}
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WeightedEdgeListVariant edges;
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if (input_file.empty()) {
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if (read_dimacs_graph(std::cin, edges) != 0) {
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if (!std::cin) {
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std::cerr << "ERROR: Can not read from stdin ("
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<< std::strerror(errno) << ")" << std::endl;
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}
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return 1;
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}
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} else {
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std::ifstream f(input_file);
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if (!f) {
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std::cerr << "ERROR: Can not open '" << input_file << "' ("
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<< std::strerror(errno) << ")" << std::endl;
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return 1;
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}
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if (read_dimacs_graph(f, edges) != 0) {
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if (!f) {
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std::cerr << "ERROR: Can not read from '" << input_file
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<< "' (" << std::strerror(errno) << ")" << std::endl;
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}
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return 1;
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}
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}
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Matching matching;
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if (edges.is_int_weight) {
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matching = run_matching(edges.int_edges);
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} else {
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matching = run_matching(edges.float_edges);
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}
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write_dimacs_matching(std::cout, matching);
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return 0;
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}
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