#582: add Dijkstra based Critical Path compute algorithm

Author: ai-mannamalai

examples/DijkstraExample/dijkstra_example.cpp

@@ -10,10 +10,10 @@ int main() {
   CXXGraph::Node<int> node2("2", 2);
   CXXGraph::Node<int> node3("3", 3);
 
-  CXXGraph::DirectedWeightedEdge<int> edge1("1", node1, node2, 2.0);
-  CXXGraph::DirectedWeightedEdge<int> edge2("2", node2, node3, 2.0);
-  CXXGraph::DirectedWeightedEdge<int> edge3("3", node0, node1, 2.0);
-  CXXGraph::DirectedWeightedEdge<int> edge4("4", node0, node3, 1.0);
+  CXXGraph::DirectedWeightedEdge<int> edge1(1, node1, node2, 2.0);
+  CXXGraph::DirectedWeightedEdge<int> edge2(2, node2, node3, 2.0);
+  CXXGraph::DirectedWeightedEdge<int> edge3(3, node0, node1, 2.0);
+  CXXGraph::DirectedWeightedEdge<int> edge4(4, node0, node3, 1.0);
 
   CXXGraph::T_EdgeSet<int> edgeSet;
   edgeSet.insert(make_shared<CXXGraph::DirectedWeightedEdge<int>>(edge1));

include/CXXGraph/Graph/Algorithm/Dijkstra_impl.hpp

@@ -598,5 +598,152 @@ const DijkstraResult Graph<T>::criticalpath_deterministic(
   return result;
 }
 
+template <typename T>
+const DijkstraResult Graph<T>::criticalpath_deterministic(
+    const Node<T>& source, const Node<T>& target) const {
+  DijkstraResult result;
+  auto nodeSet = Graph<T>::getNodeSet();
+
+  auto source_node_it = std::find_if(
+      nodeSet.begin(), nodeSet.end(),
+      [&source](auto node) { return node->getUserId() == source.getUserId(); });
+  if (source_node_it == nodeSet.end()) {
+    // check if source node exist in the graph
+    result.errorMessage = ERR_SOURCE_NODE_NOT_IN_GRAPH;
+    return result;
+  }
+
+  auto target_node_it = std::find_if(
+      nodeSet.begin(), nodeSet.end(),
+      [&target](auto node) { return node->getUserId() == target.getUserId(); });
+  if (target_node_it == nodeSet.end()) {
+    // check if target node exist in the graph
+    result.errorMessage = ERR_TARGET_NODE_NOT_IN_GRAPH;
+    return result;
+  }
+  // n denotes the number of vertices in graph
+  // unused
+  // auto n = cachedAdjMatrix->size();
+
+  // setting all the distances initially to -INF_DOUBLE
+  std::unordered_map<shared<const Node<T>>, double, nodeHash<T>> dist;
+  std::map<std::string, shared<const Node<T>>> userIds;
+
+  for (const auto& node : nodeSet) {
+    dist[node] = -INF_DOUBLE;
+    userIds[node->getUserId()] = node;
+  }
+
+  std::unordered_map<shared<const Node<T>>, size_t, nodeHash<T>> stableIds;
+  size_t index(0);
+  for (const auto& it : userIds) stableIds[it.second] = index++;
+
+  // creating a max heap using priority queue
+  // first element of pair contains the distance
+  // second element of pair contains the vertex
+
+  struct VertexInfo {
+    double distance = 0;
+    size_t sumOfIds = 0;
+    shared<const Node<T>> node;
+  };
+
+  struct VertexInfoLesser {
+    bool operator()(const VertexInfo& a, const VertexInfo& b) const {
+      if (a.distance == b.distance) return a.sumOfIds < b.sumOfIds;
+      return a.distance < b.distance;
+    };
+  };
+
+  std::priority_queue<VertexInfo, std::vector<VertexInfo>, VertexInfoLesser> pq;
+
+  // pushing the source vertex 's' with 0 distance in min heap
+  pq.push(VertexInfo{0.0, stableIds[*source_node_it], *source_node_it});
+
+  // marking the distance of source as 0
+  dist[*source_node_it] = 0;
+
+  std::unordered_map<std::string, std::string> parent;
+  parent[source.getUserId()] = "";
+
+  while (!pq.empty()) {
+    // second element of pair denotes the node / vertex
+    shared<const Node<T>> currentNode = pq.top().node;
+    // first element of pair denotes the distance
+    double currentDist = pq.top().distance;
+    auto currentNodesSum = pq.top().sumOfIds;
+
+    pq.pop();
+
+    // for all the reachable vertex from the currently exploring vertex
+    // we will try to minimize the distance
+    if (cachedAdjMatrix->find(currentNode) != cachedAdjMatrix->end()) {
+      for (const auto& elem : cachedAdjMatrix->at(currentNode)) {
+        // minimizing distances
+        if (elem.second->isWeighted().has_value() &&
+            elem.second->isWeighted().value()) {
+          if (elem.second->isDirected().has_value() &&
+              elem.second->isDirected().value()) {
+            shared<const DirectedWeightedEdge<T>> dw_edge =
+                std::static_pointer_cast<const DirectedWeightedEdge<T>>(
+                    elem.second);
+            if (dw_edge->getWeight() < 0) {
+              result.errorMessage = ERR_NEGATIVE_WEIGHTED_EDGE;
+              return result;
+            } else if (currentDist + dw_edge->getWeight() > dist[elem.first]) {
+              dist[elem.first] = currentDist + dw_edge->getWeight();
+              pq.push(VertexInfo{dist[elem.first],
+                                 currentNodesSum + stableIds[elem.first],
+                                 elem.first});
+              parent[elem.first.get()->getUserId()] =
+                  currentNode.get()->getUserId();
+            }
+          } else if (elem.second->isDirected().has_value() &&
+                     !elem.second->isDirected().value()) {
+            shared<const UndirectedWeightedEdge<T>> udw_edge =
+                std::static_pointer_cast<const UndirectedWeightedEdge<T>>(
+                    elem.second);
+            if (udw_edge->getWeight() < 0) {
+              result.errorMessage = ERR_NEGATIVE_WEIGHTED_EDGE;
+              return result;
+            } else if (currentDist + udw_edge->getWeight() > dist[elem.first]) {
+              dist[elem.first] = currentDist + udw_edge->getWeight();
+              pq.push(VertexInfo{dist[elem.first],
+                                 currentNodesSum + stableIds[elem.first],
+                                 elem.first});
+              parent[elem.first.get()->getUserId()] =
+                  currentNode.get()->getUserId();
+            }
+          } else {
+            // ERROR it shouldn't never returned ( does not exist a Node
+            // Weighted and not Directed/Undirected)
+            result.errorMessage = ERR_NO_DIR_OR_UNDIR_EDGE;
+            return result;
+          }
+        } else {
+          // No Weighted Edge
+          result.errorMessage = ERR_NO_WEIGHTED_EDGE;
+          return result;
+        }
+      }
+    }
+  }
+  if (dist[*target_node_it] != INF_DOUBLE) {
+    result.success = true;
+    result.errorMessage = "";
+    result.result = dist[*target_node_it];
+    std::string id = target.getUserId();
+    while (parent[id] != "") {
+      result.path.push_back(id);
+      id = parent[id];
+    }
+    result.path.push_back(source.getUserId());
+    std::reverse(result.path.begin(), result.path.end());
+    return result;
+  }
+  result.errorMessage = ERR_TARGET_NODE_NOT_REACHABLE;
+  return result;
+}
+
 }  // namespace CXXGraph
 #endif  // __CXXGRAPH_DIJKSTRA_IMPL_H__