From e996af75241f54298b75e0370df09744fdace793 Mon Sep 17 00:00:00 2001
From: Laurent Perron <lperron@google.com>
Date: Wed, 30 Dec 2015 00:08:16 +0100
Subject: [PATCH] incomplete version of the slitherlink problem

---
 examples/cpp/slitherlink.cc | 120 ++++++++++++++++++++++++++++++++++++
 makefiles/Makefile.cpp.mk   |   6 ++
 2 files changed, 126 insertions(+)
 create mode 100644 examples/cpp/slitherlink.cc

diff --git a/examples/cpp/slitherlink.cc b/examples/cpp/slitherlink.cc
new file mode 100644
index 0000000000..82c5422788
--- /dev/null
+++ b/examples/cpp/slitherlink.cc
@@ -0,0 +1,120 @@
+#include <vector>
+#include <string>
+
+#include "constraint_solver/constraint_solver.h"
+
+namespace operations_research {
+const std::vector<std::vector<int>> data = { {  3,  2, -1,  3 },
+                                             { -1, -1, -1,  2 },
+                                             {  3, -1, -1, -1 },
+                                             {  3, -1,  3,  1 } };
+
+const std::vector<int> zero_or_two = { 0, 2 };
+
+void PrintSolution(const std::vector<std::vector<int>>& data,
+                   const std::vector<std::vector<IntVar*>>& h_arcs,
+                   const std::vector<std::vector<IntVar*>>& v_arcs) {
+  const int num_rows = data.size();
+  const int num_columns = data[0].size();
+
+  for (int i = 0; i < num_rows; ++i) {
+    std::string first_line;
+    std::string second_line;
+    for (int j = 0; j < num_columns; ++j) {
+      const int h_arc = h_arcs[i][j]->Value();
+      const int v_arc = v_arcs[j][i]->Value();
+      const int sum = data[i][j];
+      first_line +=  h_arc == 1 ? " -" : "  ";
+      second_line += v_arc == 1 ? "|" : " ";
+      second_line += sum == -1 ? " " : StringPrintf("%d", sum).c_str();
+    }
+    const int termination = v_arcs[num_columns][i]->Value();
+    second_line += termination == 1 ? "|" : " ";
+    std::cout << first_line << std::endl;
+    std::cout << second_line << std::endl;
+  }
+  std::string last_line;
+  for (int j = 0; j < num_columns; ++j) {
+    const int h_arc = h_arcs[num_rows][j]->Value();
+    last_line +=  h_arc == 1 ? " -" : "  ";
+  }
+  std::cout << last_line << std::endl;
+}
+
+void Solve(const std::vector<std::vector<int>>& data) {
+  const int num_rows = data.size();
+  const int num_columns = data[0].size();
+
+  Solver solver("slitherlink");
+  std::vector<IntVar*> all_vars;
+  std::vector<std::vector<IntVar*>> h_arcs(num_rows + 1);
+  for (int i = 0; i < num_rows + 1; ++i) {
+    solver.MakeBoolVarArray(
+        num_columns, StringPrintf("h_arc_%i_", i), &h_arcs[i]);
+    all_vars.insert(all_vars.end(), h_arcs[i].begin(), h_arcs[i].end());
+  }
+
+  std::vector<std::vector<IntVar*>> v_arcs(num_columns + 1);
+  for (int i = 0; i < num_columns + 1; ++i) {
+    solver.MakeBoolVarArray(
+        num_rows, StringPrintf("v_arc_%i_", i), &v_arcs[i]);
+    all_vars.insert(all_vars.end(), v_arcs[i].begin(), v_arcs[i].end());
+  }
+
+  // Constraint on the sum of arcs.
+  for (int i = 0; i < num_rows; ++i) {
+    for (int j = 0; j < num_columns; ++j) {
+      const int value = data[i][j];
+      if (value != -1) {
+        std::vector<IntVar*> square = { h_arcs[i][j],
+                                        h_arcs[i + 1][j],
+                                        v_arcs[j][i],
+                                        v_arcs[j + 1][i] };
+        solver.AddConstraint(solver.MakeSumEquality(square, value));
+      }
+    }
+  }
+
+  // Hamiltonian path: each node has a degree 0 or 2.
+  for (int i = 0; i < num_rows + 1; ++i) {
+    for (int j = 0; j < num_columns + 1; ++j) {
+      std::vector<IntVar*> tmp;
+      if (j > 0) {
+        tmp.push_back(h_arcs[i][j - 1]);
+      }
+      if (j < num_columns) {
+        tmp.push_back(h_arcs[i][j]);
+      }
+      if (i > 0) {
+        tmp.push_back(v_arcs[j][i - 1]);
+      }
+      if (i < num_rows) {
+        tmp.push_back(v_arcs[j][i]);
+      }
+      solver.AddConstraint(
+          solver.MakeMemberCt(solver.MakeSum(tmp), zero_or_two));
+    }
+  }
+
+  // Hamiltonian path: add single path constraint.
+
+  // Search.
+  DecisionBuilder* const db =
+      solver.MakePhase(all_vars,
+                       Solver::CHOOSE_FIRST_UNBOUND,
+                       Solver::ASSIGN_MAX_VALUE);
+
+  SearchMonitor* const log = solver.MakeSearchLog(1000000);
+
+  solver.NewSearch(db, log);
+  while (solver.NextSolution()) {
+    PrintSolution(data, h_arcs, v_arcs);
+  }
+  solver.EndSearch();
+}
+}  // namespace operations_research
+
+int main() {
+  operations_research::Solve(operations_research::data);
+  return 0;
+}
diff --git a/makefiles/Makefile.cpp.mk b/makefiles/Makefile.cpp.mk
index 8c3ce25474..456e20c839 100644
--- a/makefiles/Makefile.cpp.mk
+++ b/makefiles/Makefile.cpp.mk
@@ -1352,6 +1352,12 @@ $(OBJ_DIR)/pdptw.$O: $(EX_DIR)/cpp/pdptw.cc $(SRC_DIR)/constraint_solver/constra
 $(BIN_DIR)/pdptw$E: $(DYNAMIC_ROUTING_DEPS) $(OBJ_DIR)/pdptw.$O
 	$(CCC) $(CFLAGS) $(OBJ_DIR)/pdptw.$O $(DYNAMIC_ROUTING_LNK) $(DYNAMIC_LD_FLAGS) $(EXE_OUT)$(BIN_DIR)$Spdptw$E
 
+$(OBJ_DIR)/slitherlink.$O:$(EX_DIR)/cpp/slitherlink.cc $(SRC_DIR)/constraint_solver/constraint_solver.h
+	$(CCC) $(CFLAGS) -c $(EX_DIR)$Scpp/slitherlink.cc $(OBJ_OUT)$(OBJ_DIR)$Sslitherlink.$O
+
+$(BIN_DIR)/slitherlink$E: $(DYNAMIC_CP_DEPS) $(OBJ_DIR)/slitherlink.$O
+	$(CCC) $(CFLAGS) $(OBJ_DIR)/slitherlink.$O $(DYNAMIC_CP_LNK) $(DYNAMIC_LD_FLAGS) $(EXE_OUT)$(BIN_DIR)$Sslitherlink$E
+
 $(OBJ_DIR)/sports_scheduling.$O:$(EX_DIR)/cpp/sports_scheduling.cc $(SRC_DIR)/constraint_solver/constraint_solver.h
 	$(CCC) $(CFLAGS) -c $(EX_DIR)$Scpp/sports_scheduling.cc $(OBJ_OUT)$(OBJ_DIR)$Ssports_scheduling.$O