making dist and prev maps into 1, as they are accessed together always, for performance reasons.

lib/graph/graph_algorithms.hpp

@@ -7,35 +7,38 @@
 #include <unordered_map>
 #include <unordered_set>
 #include <queue>
+#include <set>
 
 #include <utility>
 #include <algorithm>
 #include <functional>
+#include <type_traits>
 
 
 namespace {
 
 template <typename V, typename W>
-inline V closestNode(const std::unordered_set<V>& q, const std::unordered_map<V, W>& dist)
+inline V closestNode(const std::unordered_set<V>& q, const std::unordered_map<V, std::pair<W, V> >& dist_prev)
 {
   const typename std::unordered_set<V>::const_iterator smallest_it =
     std::min_element(q.begin(), q.end(),
-      [&dist](const V& v1, const V& v2)
-      { return !(  dist.find(v2) != dist.end() &&
-                   ((dist.find(v1) == dist.end()) || (dist.at(v1) > dist.at(v2)))  ); } );
+      [&dist_prev](const V& v1, const V& v2)
+      { const auto v1_it = dist_prev.find(v1);
+        const auto v2_it = dist_prev.find(v2);
+        return !(  v2_it != dist_prev.end() && ((v1_it == dist_prev.end()) || (v1_it->second.first > v2_it->second.first))  ); } );
 
   return *smallest_it;
 }
 
-template <typename V>
-std::vector<V> pathFromPrevList(const V& dest, std::unordered_map<V, V> prev)
+template <typename V, typename W>
+std::vector<V> pathFromPrevList(const V& dest, const std::unordered_map<V, std::pair<W, V> >& dist_prev)
 {
   std::vector<V> retval;
-  if (prev.find(dest) == prev.end())
+  if (dist_prev.find(dest) == dist_prev.end())
     return retval;
 
   V it = dest;
-  for (; prev.find(it) != prev.end() ; it = prev.at(it)) {
+  for (; it != V() ; it = dist_prev.at(it).second) {
     retval.push_back(it);
   }
   retval.push_back(it);
@@ -54,39 +57,36 @@ dijkstra_shortest_path_to(const Graph<V>& graph,
                           const V& dest,
                           std::function<W(V, V)> distanceCompute)
 {
-  std::unordered_map<V, W> dist;
-  std::unordered_map<V, V> prev;
+  std::unordered_map<V, std::pair<W, V> > dist_prev;
 
-  dist.emplace(source, W());
+  dist_prev.emplace(source, std::pair<W, V>(W(), V()));
   std::unordered_set<V> q;
   for (const auto& v : graph.neighboursOf(source)) {
     q.insert(v);
-    dist[v] = distanceCompute(source, v);
-    prev[v] = source;
+    dist_prev.emplace(v, std::pair<W, V>(distanceCompute(source, v), source));
   }
 
   while (!q.empty()) {
-    const V& u = closestNode<V, W>(q, dist);
+    const V& u = closestNode<V, W>(q, dist_prev);
     q.erase(u);
     if (u == dest)
       break;
 
-    for (V v : graph.neighboursOf(u)) {
+    for (const auto& v : graph.neighboursOf(u)) {
       const W d = distanceCompute(u, v);
-      const W alt = dist.at(u) + d;
+      const W alt = dist_prev.at(u).first + d;
 
-      if (dist.find(v) == dist.end()) { // new node
-        dist.emplace(v, alt);
-        prev.emplace(v, u);
+      if (dist_prev.find(v) == dist_prev.end()) { // new node
+        dist_prev.emplace(v, std::pair<W, V>(alt, u));
         q.insert(v);
-      } else if (alt < dist.at(v)) { // better route
-        dist[v] = alt;
-        prev[v] = u;
+      } else if (alt < dist_prev.at(v).first) { // better route
+        dist_prev[v] = std::pair<W, V>(alt, u);
       }
     }
   }
 
-  return pathFromPrevList(dest, prev);
+  return pathFromPrevList(dest, dist_prev);
 }
 
+
 #endif // GRAPH_ALGORITHMS_HPP

test/graph/test_graph_algorithms.cpp

@@ -5,6 +5,8 @@
 
 #include "fixture.hpp"
 
+#include <iostream>
+
 void printPath(std::size_t number_of_rows,
                std::size_t number_of_columns,
                float2 source,
@@ -48,7 +50,7 @@ TEST_CASE("Graph algorithms, small", "[graph][algorithm][dijkstra]" ) {
     Graph<int> g;
     const int source(0);
     const int destination(1);
-    const std::vector<int> shortestPath = dijkstra_shortest_path_to<int, int>(g, source, destination, std::distanceOf2ints());
+    const std::vector<int> shortestPath = dijkstra_shortest_path_to(g, source, destination, std::distanceOf2ints());
     REQUIRE( shortestPath.size() == 0 );
   }
 
@@ -56,7 +58,7 @@ TEST_CASE("Graph algorithms, small", "[graph][algorithm][dijkstra]" ) {
     Graph<int> g = { {1, 2}, {1, 3}, {1, 4}, {2, 4}, {3, 4} };
     const int source(1);
     const int destination(10);
-    const std::vector<int> shortestPath = dijkstra_shortest_path_to<int, int>(g, source, destination, std::distanceOf2ints());
+    const std::vector<int> shortestPath = dijkstra_shortest_path_to(g, source, destination, std::distanceOf2ints());
     REQUIRE( shortestPath.size() == 0 );
   }
 
@@ -64,7 +66,7 @@ TEST_CASE("Graph algorithms, small", "[graph][algorithm][dijkstra]" ) {
     Graph<int> g = { {1, 2}, {1, 3}, {1, 4}, {2, 4}, {3, 4} };
     const int source(10);
     const int destination(1);
-    const std::vector<int> shortestPath = dijkstra_shortest_path_to<int, int>(g, source, destination, std::distanceOf2ints());
+    const std::vector<int> shortestPath = dijkstra_shortest_path_to(g, source, destination, std::distanceOf2ints());
     REQUIRE( shortestPath.size() == 0 );
   }
 
@@ -72,7 +74,7 @@ TEST_CASE("Graph algorithms, small", "[graph][algorithm][dijkstra]" ) {
     Graph<int> g = { {1, 2}, {3, 4} };
     const int source(1);
     const int destination(4);
-    const std::vector<int> shortestPath = dijkstra_shortest_path_to<int, int>(g, source, destination, std::distanceOf2ints());
+    const std::vector<int> shortestPath = dijkstra_shortest_path_to(g, source, destination, std::distanceOf2ints());
     REQUIRE( shortestPath.size() == 0 );
   }
 
@@ -84,7 +86,7 @@ TEST_CASE("Graph algorithms, small", "[graph][algorithm][dijkstra]" ) {
 
     const float2 source(0, 0);
     const float2 destination(2, 2);
-    const std::vector<float2> shortestPath = dijkstra_shortest_path_to<float2, float>(g, source, destination, std::distanceOf2float2s());
+    const std::vector<float2> shortestPath = dijkstra_shortest_path_to(g, source, destination, std::distanceOf2float2s());
 
     const float euclidan_distance = sqrt(pow(source.x - destination.x, 2) + pow(source.y - destination.y, 2));
     REQUIRE( std::distanceOf2float2s()(source, destination) == euclidan_distance );
@@ -112,7 +114,7 @@ TEST_CASE_METHOD(Fixture<float2>, "Graph algorithms, big graph", "[graph][algori
 
     const float2 source(0, 0);
     const float2 destination(number_of_rows-1, number_of_columns-1);
-    const std::vector<float2> shortestPath = dijkstra_shortest_path_to<float2, float>(g, source, destination, std::distanceOf2float2s());
+    const std::vector<float2> shortestPath = dijkstra_shortest_path_to(g, source, destination, std::distanceOf2float2s());
 
     REQUIRE( shortestPath.size() == number_of_rows);
     for (std::size_t i = 0; i < number_of_rows; ++i)