polish examples

examples/cpp/binpacking_2d_sat.cc

@@ -170,6 +170,22 @@ absl::btree_set<int> FindFixedItems(
   return fixed_items;
 }
 
+// Solves a subset sum problem to find the maximum reachable max size.
+int64_t MaxSubsetSumSize(const std::vector<int64_t>& sizes, int64_t max_size) {
+  CpModelBuilder builder;
+  LinearExpr weighed_sum;
+  for (const int size : sizes) {
+    BoolVar var = builder.NewBoolVar();
+    weighed_sum += size * var;
+  }
+
+  builder.AddLessOrEqual(weighed_sum, max_size);
+  builder.Maximize(weighed_sum);
+
+  const CpSolverResponse response = Solve(builder.Build());
+  return static_cast<int64_t>(response.objective_value());
+}
+
 }  // namespace
 
 // Load a 2D bin packing problem and solve it.
@@ -184,8 +200,8 @@ void LoadAndSolve(const std::string& file_name, int instance) {
             << file_name << "'";
   LOG(INFO) << "Instance has " << problem.items_size() << " items";
 
-  const auto bin_sizes = problem.box_shape().dimensions();
-  const int num_dimensions = bin_sizes.size();
+  const auto original_bin_sizes = problem.box_shape().dimensions();
+  const int num_dimensions = original_bin_sizes.size();
   const int num_items = problem.items_size();
 
   // Non overlapping.
@@ -195,14 +211,23 @@ void LoadAndSolve(const std::string& file_name, int instance) {
     LOG(FATAL) << num_dimensions << " dimensions not supported.";
   }
 
-  const int64_t area_of_one_bin = bin_sizes[0] * bin_sizes[1];
+  // Reduce the size of the box with subset-sum.
+  std::vector<int64_t> x_sizes;
+  std::vector<int64_t> y_sizes;
   int64_t sum_of_items_area = 0;
   for (const auto& item : problem.items()) {
     CHECK_EQ(1, item.shapes_size());
     const auto& shape = item.shapes(0);
     CHECK_EQ(2, shape.dimensions_size());
     sum_of_items_area += shape.dimensions(0) * shape.dimensions(1);
+    x_sizes.push_back(shape.dimensions(0));
+    y_sizes.push_back(shape.dimensions(1));
   }
+  std::vector<int64_t> bin_sizes(2);
+  bin_sizes[0] = MaxSubsetSumSize(x_sizes, original_bin_sizes[0]);
+  bin_sizes[1] = MaxSubsetSumSize(y_sizes, original_bin_sizes[1]);
+
+  const int64_t area_of_one_bin = bin_sizes[0] * bin_sizes[1];
 
   const int64_t trivial_lb = CeilOfRatio(sum_of_items_area, area_of_one_bin);
   LOG(INFO) << "Trivial lower bound of the number of bins = " << trivial_lb;
@@ -270,8 +295,7 @@ void LoadAndSolve(const std::string& file_name, int instance) {
   }
 
   // Compute the min size of all items in each dimension.
-  std::vector<int64_t> min_sizes_per_dimension = {bin_sizes.begin(),
-                                                  bin_sizes.end()};
+  std::vector<int64_t> min_sizes_per_dimension = bin_sizes;
   for (int item = 0; item < num_items; ++item) {
     for (int dim = 0; dim < num_dimensions; ++dim) {
       min_sizes_per_dimension[dim] =
@@ -295,14 +319,12 @@ void LoadAndSolve(const std::string& file_name, int instance) {
         const int64_t size = problem.items(item).shapes(0).dimensions(dim);
         IntVar start;
         if (b == 0) {
-          // For item fixed to a given bin, by symmetry of rotation we can also
-          // assume it is in the lower left corner.
-          // Note that the data defines the global size, so the range of the
-          // interval is [0, bin_size - 1].
+          // For item fixed to a given bin, by symmetry, we can also assume it
+          // is in the lower left corner.
           const int64_t start_max = fixed_items.contains(item)
-                                        ? (bin_size - size) / 2
-                                        : bin_size - 1 - size;
-	  start = cp_model.NewIntVar({0, start_max});
+                                        ? (bin_size - size + 1) / 2
+                                        : bin_size - size;
+          start = cp_model.NewIntVar({0, start_max});
           starts_by_dimension[item][dim] = start;
 
           if (size + min_sizes_per_dimension[dim] > bin_size) {
@@ -351,7 +373,14 @@ void LoadAndSolve(const std::string& file_name, int instance) {
   }
 
   // Non overlapping.
-  LOG(INFO) << "Box size: " << bin_sizes[0] << "*" << bin_sizes[1];
+  if (bin_sizes[0] == original_bin_sizes[0] &&
+      bin_sizes[1] == original_bin_sizes[1]) {
+    LOG(INFO) << "Box size: [" << bin_sizes[0] << " * " << bin_sizes[1] << "]";
+  } else {
+    LOG(INFO) << "Box size: [" << bin_sizes[0] << " * " << bin_sizes[1]
+              << "] reduced from [" << original_bin_sizes[0] << " * "
+              << original_bin_sizes[1] << "]";
+  }
   for (int b = 0; b < max_bins; ++b) {
     NoOverlap2DConstraint no_overlap_2d = cp_model.AddNoOverlap2D();
     for (int item = 0; item < num_items; ++item) {

examples/cpp/costas_array_sat.cc

@@ -31,6 +31,7 @@
 #include "absl/flags/flag.h"
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_format.h"
+#include "absl/types/span.h"
 #include "ortools/base/init_google.h"
 #include "ortools/base/logging.h"
 #include "ortools/base/types.h"
@@ -48,7 +49,7 @@ namespace operations_research {
 namespace sat {
 
 // Checks that all pairwise distances are unique and returns all violators
-void CheckConstraintViolators(const std::vector<int64_t>& vars,
+void CheckConstraintViolators(absl::Span<const int64_t> vars,
                               std::vector<int>* const violators) {
   int dim = vars.size();