set_cover: backport from main

ortools/algorithms/README.md

@@ -2,69 +2,6 @@
 
 This directory contains data structures and algorithms for various problems.
 
-## Set covering
-
-An instance of set covering is composed of two entities: elements and sets; sets
-cover a series of elements. The problem of set covering is about finding the
-cheapest combination of sets that cover all the elements.
-
-[More information on Wikipedia](https://en.wikipedia.org/wiki/Set_cover_problem).
-
-*   Solver: [`set_cover_heuristics.h`](set_cover_heuristics.h).
-*   Instance representation: [`set_cover_model.h`](set_cover_model.h).
-*   Instance parser: [`set_cover_reader.h`](set_cover_reader.h).
-
-Create an instance:
-
-```cpp
-// If the elements are integers, a subset can be a std::vector<int> (in a pair
-// along its cost).
-std::vector<std::pair<std::vector<int>, int>> subsets = ...;
-
-SetCoverModel model;
-for (const auto [subset, subset_cost] : subsets) {
-  model.AddEmptySubset(subset_cost)
-  for (const int element : subset) {
-    model.AddElementToLastSubset(element);
-  }
-}
-SetCoverLedger ledger(&model);
-```
-
-Solve it using a MIP solver (guarantees to yield the optimum solution if it has
-enough time to run):
-
-```cpp
-SetCoverMip mip(&ledger);
-mip.SetTimeLimitInSeconds(10);
-mip.NextSolution();
-SubsetBoolVector best_choices = ledger.GetSolution();
-LOG(INFO) << "Cost: " << ledger.cost();
-```
-
-A custom combination of heuristics (10,000 iterations of: clearing 10% of the
-variables, running a Chvatal greedy descent, using steepest local search):
-
-```cpp
-Cost best_cost = std::numeric_limits<Cost>::max();
-SubsetBoolVector best_choices = ledger.GetSolution();
-for (int i = 0; i < 10000; ++i) {
-  ledger.LoadSolution(best_choices);
-  ClearRandomSubsets(0.1 * model.num_subsets().value(), &ledger);
-
-  GreedySolutionGenerator greedy(&ledger);
-  CHECK(greedy.NextSolution());
-
-  SteepestSearch steepest(&ledger);
-  CHECK(steepest.NextSolution(10000));
-
-  EXPECT_TRUE(ledger.CheckSolution());
-  if (ledger.cost() < best_cost) {
-    best_cost = ledger.cost();
-    best_choices = ledger.GetSolution();
-    LOG(INFO) << "Better cost: " << best_cost << " at iteration = " << i;
-  }
-}
-ledger.LoadSolution(best_choices);
-LOG(INFO) << "Best cost: " << ledger.cost();
-```
+It used to contain a solver for set covering, which has moved to the
+[set_cover](../set_cover)
+folder.