C++ Library for Competitive Programming
#include "emthrm/graph/traveling_salesman_problem.hpp"
重み付き有向グラフに対してコスト最小のハミルトン閉路を求める問題である。
$O(2^{\lvert V \rvert} {\lvert V \rvert}^2)$
名前 | 戻り値 |
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template <typename CostType> CostType traveling_salesman_problem(const std::vector<std::vector<Edge<CostType>>>& graph, const CostType inf = std::numeric_limits<CostType>::max());
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グラフ $\mathrm{graph}$ の巡回セールスマン問題の解のコスト。ただし解が存在しないときは $\infty$ を返す。 |
Held–Karp algorithm
#ifndef EMTHRM_GRAPH_TRAVELING_SALESMAN_PROBLEM_HPP_
#define EMTHRM_GRAPH_TRAVELING_SALESMAN_PROBLEM_HPP_
#include <algorithm>
#include <limits>
#include <numeric>
#include <vector>
#include "emthrm/graph/edge.hpp"
namespace emthrm {
template <typename CostType>
CostType traveling_salesman_problem(
const std::vector<std::vector<Edge<CostType>>>& graph,
const CostType inf = std::numeric_limits<CostType>::max()) {
const int n = graph.size();
if (n == 1) [[unlikely]] return 0;
std::vector<std::vector<CostType>> dp(1 << n, std::vector<CostType>(n, inf));
dp[1][0] = 0;
for (int i = 1; i < (1 << n); ++i) {
for (int j = 0; j < n; ++j) {
if (dp[i][j] == inf) continue;
for (const Edge<CostType>& e : graph[j]) {
if (i >> e.dst & 1) continue;
dp[i | (1 << e.dst)][e.dst] =
std::min(dp[i | (1 << e.dst)][e.dst], dp[i][j] + e.cost);
}
}
}
CostType res = inf;
for (int j = 1; j < n; ++j) {
if (dp.back()[j] == inf) continue;
for (const Edge<CostType>& e : graph[j]) {
if (e.dst == 0) res = std::min(res, dp.back()[j] + e.cost);
}
}
return res;
}
} // namespace emthrm
#endif // EMTHRM_GRAPH_TRAVELING_SALESMAN_PROBLEM_HPP_
#line 1 "include/emthrm/graph/traveling_salesman_problem.hpp"
#include <algorithm>
#include <limits>
#include <numeric>
#include <vector>
#line 1 "include/emthrm/graph/edge.hpp"
/**
* @title 辺
*/
#ifndef EMTHRM_GRAPH_EDGE_HPP_
#define EMTHRM_GRAPH_EDGE_HPP_
#include <compare>
namespace emthrm {
template <typename CostType>
struct Edge {
CostType cost;
int src, dst;
explicit Edge(const int src, const int dst, const CostType cost = 0)
: cost(cost), src(src), dst(dst) {}
auto operator<=>(const Edge& x) const = default;
};
} // namespace emthrm
#endif // EMTHRM_GRAPH_EDGE_HPP_
#line 10 "include/emthrm/graph/traveling_salesman_problem.hpp"
namespace emthrm {
template <typename CostType>
CostType traveling_salesman_problem(
const std::vector<std::vector<Edge<CostType>>>& graph,
const CostType inf = std::numeric_limits<CostType>::max()) {
const int n = graph.size();
if (n == 1) [[unlikely]] return 0;
std::vector<std::vector<CostType>> dp(1 << n, std::vector<CostType>(n, inf));
dp[1][0] = 0;
for (int i = 1; i < (1 << n); ++i) {
for (int j = 0; j < n; ++j) {
if (dp[i][j] == inf) continue;
for (const Edge<CostType>& e : graph[j]) {
if (i >> e.dst & 1) continue;
dp[i | (1 << e.dst)][e.dst] =
std::min(dp[i | (1 << e.dst)][e.dst], dp[i][j] + e.cost);
}
}
}
CostType res = inf;
for (int j = 1; j < n; ++j) {
if (dp.back()[j] == inf) continue;
for (const Edge<CostType>& e : graph[j]) {
if (e.dst == 0) res = std::min(res, dp.back()[j] + e.cost);
}
}
return res;
}
} // namespace emthrm