87 lines
2.7 KiB
C++
87 lines
2.7 KiB
C++
// Copyright 2011-2014 Google
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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//
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// n-Queens Problem
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//
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// Implementation of a basic model to fetch the first feasible solution.
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#include "base/commandlineflags.h"
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#include "base/logging.h"
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#include "base/stringprintf.h"
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#include "nqueens_utilities.h"
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DEFINE_int32(size, 0,
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"Size of the problem. If equal to 0, will test several increasing sizes.");
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DECLARE_bool(use_symmetry);
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namespace operations_research {
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void NQueens(int size) {
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CHECK_GE(size, 1);
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Solver s("nqueens");
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// model
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std::vector<IntVar*> queens;
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for (int i = 0; i < size; ++i) {
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queens.push_back(s.MakeIntVar(0, size - 1, StringPrintf("queen%04d", i)));
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}
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s.AddConstraint(s.MakeAllDifferent(queens));
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std::vector<IntVar*> vars(size);
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for (int i = 0; i < size; ++i) {
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vars[i] = s.MakeSum(queens[i], i)->Var();
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}
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s.AddConstraint(s.MakeAllDifferent(vars));
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for (int i = 0; i < size; ++i) {
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vars[i] = s.MakeSum(queens[i], -i)->Var();
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}
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s.AddConstraint(s.MakeAllDifferent(vars));
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SolutionCollector* const collector = s.MakeFirstSolutionCollector();
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collector->Add(queens);
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DecisionBuilder* const db = s.MakePhase(queens,
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Solver::CHOOSE_FIRST_UNBOUND,
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Solver::ASSIGN_MIN_VALUE);
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s.Solve(db, collector); // go!
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const int num_solutions = collector->solution_count();
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CHECK_LE(num_solutions, 1);
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const int64 time = s.wall_time();
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std::cout << "============================" << std::endl;
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std::cout << "size: " << size << std::endl;
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std::cout << "The Solve method took "
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<< time/1000.0 << " seconds" << std::endl;
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std::cout << "number of solutions: " << num_solutions << std::endl;
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PrintFirstSolution(size, queens, collector);
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}
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} // namespace operations_research
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int main(int argc, char **argv) {
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google::ParseCommandLineFlags(&argc, &argv, true);
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if (FLAGS_use_symmetry) {
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LOG(FATAL) << "Symmetries not yet implemented!";
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}
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if (FLAGS_size != 0) {
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operations_research::NQueens(FLAGS_size);
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} else {
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for (int n = 1; n < 12; ++n) {
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operations_research::NQueens(n);
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}
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}
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return 0;
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}
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