add sanity check for identical start states

This needs to be on the example-level, because the generic (E)CBS
implementation actually has no notion of time and conflicts as well as
constraints are abstract, templated types (only known by the low-level
search).

example/cbs.cpp

@@ -627,6 +627,16 @@ int main(int argc, char* argv[]) {
     goals.emplace_back(Location(goal[0].as<int>(), goal[1].as<int>()));
   }
 
+  // sanity check: no identical start states
+  std::unordered_set<State> startStatesSet;
+  for (const auto& s : startStates) {
+    if (startStatesSet.find(s) != startStatesSet.end()) {
+      std::cout << "Identical start states detected -> no solution!" << std::endl;
+      return 0;
+    }
+    startStatesSet.insert(s);
+  }
+
   Environment mapf(dimx, dimy, obstacles, goals, disappearAtGoal);
   CBS<State, Action, int, Conflict, Constraints, Environment> cbs(mapf);
   std::vector<PlanResult<State, Action, int> > solution;

example/cbs_ta.cpp

@@ -567,6 +567,16 @@ int main(int argc, char* argv[]) {
     }
   }
 
+  // sanity check: no identical start states
+  std::unordered_set<State> startStatesSet;
+  for (const auto& s : startStates) {
+    if (startStatesSet.find(s) != startStatesSet.end()) {
+      std::cout << "Identical start states detected -> no solution!" << std::endl;
+      return 0;
+    }
+    startStatesSet.insert(s);
+  }
+
   Environment mapf(dimx, dimy, obstacles, startStates, goals,
                    maxTaskAssignments);
   CBSTA<State, Action, int, Conflict, Constraints, Location, Environment>

example/ecbs.cpp

@@ -585,6 +585,16 @@ int main(int argc, char* argv[]) {
     goals.emplace_back(Location(goal[0].as<int>(), goal[1].as<int>()));
   }
 
+  // sanity check: no identical start states
+  std::unordered_set<State> startStatesSet;
+  for (const auto& s : startStates) {
+    if (startStatesSet.find(s) != startStatesSet.end()) {
+      std::cout << "Identical start states detected -> no solution!" << std::endl;
+      return 0;
+    }
+    startStatesSet.insert(s);
+  }
+
   Environment mapf(dimx, dimy, obstacles, goals, disappearAtGoal);
   ECBS<State, Action, int, Conflict, Constraints, Environment> ecbs(mapf, w);
   std::vector<PlanResult<State, Action, int> > solution;

example/ecbs_ta.cpp

@@ -641,6 +641,16 @@ int main(int argc, char* argv[]) {
     }
   }
 
+  // sanity check: no identical start states
+  std::unordered_set<State> startStatesSet;
+  for (const auto& s : startStates) {
+    if (startStatesSet.find(s) != startStatesSet.end()) {
+      std::cout << "Identical start states detected -> no solution!" << std::endl;
+      return 0;
+    }
+    startStatesSet.insert(s);
+  }
+
   Environment mapf(dimx, dimy, obstacles, startStates, goals,
                    maxTaskAssignments);
   ECBSTA<State, Action, int, Conflict, Constraints, Location,