76 lines
2.5 KiB
C++
76 lines
2.5 KiB
C++
// Copyright 2010-2017 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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// N-queens problem
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//
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// unique solutions: http://www.research.att.com/~njas/sequences/A000170
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// distinct solutions: http://www.research.att.com/~njas/sequences/A002562
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#include "ortools/base/commandlineflags.h"
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#include "ortools/base/integral_types.h"
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#include "ortools/base/logging.h"
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#include "ortools/base/stringprintf.h"
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#include "ortools/constraint_solver/constraint_solver.h"
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DEFINE_int32(
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size, 0,
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"Size of the problem. If equal to 0, will test several increasing sizes.");
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namespace operations_research {
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void NQueens(int size) {
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printf("========= size: %d\n", 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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for (int i = 0; i < size - 1; ++i) {
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for (int j = i + 1; j < size; ++j) {
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s.AddConstraint(s.MakeNonEquality(queens[i], queens[j]));
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s.AddConstraint(
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s.MakeNonEquality(s.MakeSum(queens[i], i), s.MakeSum(queens[j], j)));
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s.AddConstraint(s.MakeNonEquality(
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s.MakeSum(queens[i], -i), s.MakeSum(queens[j], -j)));
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}
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}
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std::vector<SearchMonitor*> monitors;
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DecisionBuilder* const db = s.MakePhase(queens, Solver::CHOOSE_FIRST_UNBOUND,
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Solver::ASSIGN_MIN_VALUE);
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s.NewSearch(db, monitors);
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int num_solutions = 0;
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while (s.NextSolution()) {
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num_solutions++;
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}
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s.EndSearch();
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printf("========= number of solutions:%d\n", num_solutions);
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printf(" number of failures: %lld\n", s.failures());
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printf(" time: %lld ms\n", s.wall_time());
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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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gflags::ParseCommandLineFlags(&argc, &argv, true);
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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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