Add missing basic examples

C++:
 - [Up] linear_programming
 - [Up] integer_programming
 - constraint_programming_CP / rabbits_pheasants_cp
 - knapsack
 - max_flow / min_cost_flow
 - tsp / vrp
note: previous "fuzzy" tsp has been renamed random_tsp.

.Net:
 - vrp

examples/cpp/random_tsp.cc

@@ -0,0 +1,167 @@
+// Copyright 2010-2017 Google
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//
+// Traveling Salesman Sample.
+//
+// This is a sample using the routing library to solve a Traveling Salesman
+// Problem.
+// The description of the problem can be found here:
+// http://en.wikipedia.org/wiki/Travelling_salesman_problem.
+// For small problems one can use the hamiltonian path library directly (cf
+// graph/hamiltonian_path.h).
+// The optimization engine uses local search to improve solutions, first
+// solutions being generated using a cheapest addition heuristic.
+// Optionally one can randomly forbid a set of random connections between nodes
+// (forbidden arcs).
+
+#include <memory>
+
+#include "google/protobuf/text_format.h"
+#include "ortools/base/callback.h"
+#include "ortools/base/commandlineflags.h"
+#include "ortools/base/integral_types.h"
+#include "ortools/base/join.h"
+#include "ortools/base/random.h"
+#include "ortools/constraint_solver/routing.h"
+#include "ortools/constraint_solver/routing_enums.pb.h"
+#include "ortools/constraint_solver/routing_flags.h"
+
+DEFINE_int32(tsp_size, 10, "Size of Traveling Salesman Problem instance.");
+DEFINE_bool(tsp_use_random_matrix, true, "Use random cost matrix.");
+DEFINE_int32(tsp_random_forbidden_connections, 0,
+             "Number of random forbidden connections.");
+DEFINE_bool(tsp_use_deterministic_random_seed, false,
+            "Use deterministic random seeds.");
+
+namespace operations_research {
+
+// Random seed generator.
+int32 GetSeed() {
+  if (FLAGS_tsp_use_deterministic_random_seed) {
+    return ACMRandom::DeterministicSeed();
+  } else {
+    return ACMRandom::HostnamePidTimeSeed();
+  }
+}
+
+// Cost/distance functions.
+
+// Sample function.
+int64 MyDistance(RoutingModel::NodeIndex from, RoutingModel::NodeIndex to) {
+  // Put your distance code here.
+  return (from + to).value();  // for instance
+}
+
+// Random matrix.
+class RandomMatrix {
+ public:
+  explicit RandomMatrix(int size) : size_(size) {}
+  void Initialize() {
+    matrix_.reset(new int64[size_ * size_]);
+    const int64 kDistanceMax = 100;
+    ACMRandom randomizer(GetSeed());
+    for (RoutingModel::NodeIndex from = RoutingModel::kFirstNode; from < size_;
+         ++from) {
+      for (RoutingModel::NodeIndex to = RoutingModel::kFirstNode; to < size_;
+           ++to) {
+        if (to != from) {
+          matrix_[MatrixIndex(from, to)] = randomizer.Uniform(kDistanceMax);
+        } else {
+          matrix_[MatrixIndex(from, to)] = 0LL;
+        }
+      }
+    }
+  }
+  int64 Distance(RoutingModel::NodeIndex from,
+                 RoutingModel::NodeIndex to) const {
+    return matrix_[MatrixIndex(from, to)];
+  }
+
+ private:
+  int64 MatrixIndex(RoutingModel::NodeIndex from,
+                    RoutingModel::NodeIndex to) const {
+    return (from * size_ + to).value();
+  }
+  std::unique_ptr<int64[]> matrix_;
+  const int size_;
+};
+
+void Tsp() {
+  if (FLAGS_tsp_size > 0) {
+    // TSP of size FLAGS_tsp_size.
+    // Second argument = 1 to build a single tour (it's a TSP).
+    // Nodes are indexed from 0 to FLAGS_tsp_size - 1, by default the start of
+    // the route is node 0.
+    RoutingModel routing(FLAGS_tsp_size, 1, RoutingModel::NodeIndex(0));
+    RoutingSearchParameters parameters = BuildSearchParametersFromFlags();
+    // Setting first solution heuristic (cheapest addition).
+    parameters.set_first_solution_strategy(
+        FirstSolutionStrategy::PATH_CHEAPEST_ARC);
+
+    // Setting the cost function.
+    // Put a permanent callback to the distance accessor here. The callback
+    // has the following signature: ResultCallback2<int64, int64, int64>.
+    // The two arguments are the from and to node inidices.
+    RandomMatrix matrix(FLAGS_tsp_size);
+    if (FLAGS_tsp_use_random_matrix) {
+      matrix.Initialize();
+      routing.SetArcCostEvaluatorOfAllVehicles(
+          NewPermanentCallback(&matrix, &RandomMatrix::Distance));
+    } else {
+      routing.SetArcCostEvaluatorOfAllVehicles(
+          NewPermanentCallback(MyDistance));
+    }
+    // Forbid node connections (randomly).
+    ACMRandom randomizer(GetSeed());
+    int64 forbidden_connections = 0;
+    while (forbidden_connections < FLAGS_tsp_random_forbidden_connections) {
+      const int64 from = randomizer.Uniform(FLAGS_tsp_size - 1);
+      const int64 to = randomizer.Uniform(FLAGS_tsp_size - 1) + 1;
+      if (routing.NextVar(from)->Contains(to)) {
+        LOG(INFO) << "Forbidding connection " << from << " -> " << to;
+        routing.NextVar(from)->RemoveValue(to);
+        ++forbidden_connections;
+      }
+    }
+    // Solve, returns a solution if any (owned by RoutingModel).
+    const Assignment* solution = routing.SolveWithParameters(parameters);
+    if (solution != nullptr) {
+      // Solution cost.
+      LOG(INFO) << "Cost " << solution->ObjectiveValue();
+      // Inspect solution.
+      // Only one route here; otherwise iterate from 0 to routing.vehicles() - 1
+      const int route_number = 0;
+      std::string route;
+      for (int64 node = routing.Start(route_number); !routing.IsEnd(node);
+           node = solution->Value(routing.NextVar(node))) {
+        absl::StrAppend(&route, routing.IndexToNode(node).value(), " (", node,
+                        ") -> ");
+      }
+      const int64 end = routing.End(route_number);
+      absl::StrAppend(&route, routing.IndexToNode(end).value(), " (", end, ")");
+      LOG(INFO) << route;
+    } else {
+      LOG(INFO) << "No solution found.";
+    }
+  } else {
+    LOG(INFO) << "Specify an instance size greater than 0.";
+  }
+}
+}  // namespace operations_research
+
+int main(int argc, char** argv) {
+  gflags::ParseCommandLineFlags(&argc, &argv, true);
+  operations_research::Tsp();
+  return 0;
+}