priority_queue.hpp with ineffective modifyKey

lib/graph/priority_queue.hpp

@@ -0,0 +1,51 @@
+#ifndef PRIORITY_QUEUE_HPP
+#define PRIORITY_QUEUE_HPP
+
+#include <map> // std::m_map
+#include <algorithm> // std::find_if
+
+/** @brief Priority Queu with top, push, pop, modifyKey.
+ *
+ * The priority queue based Dijkstra (shortest path) algorith requires the
+ * modifyKey functionality, which the std::priority_queue does not have.
+ *
+ * @note modifyKey is very ineffective, since std::map is not a
+ * bidirectional map, looking up an element based on value is linear.
+ *
+ * @todo replace std::map with a Fibonacci heap to improve performance.
+ */
+
+template <
+  typename Key,
+  typename T,
+  typename Compare = std::less<Key>,
+  typename Allocator = std::allocator<std::pair<const Key, T> >
+>
+class PriorityQueue
+{
+public:
+
+  PriorityQueue() : m_map() {}
+
+  // capacity
+  size_t size() const { return m_map.size(); }
+  bool empty() const { return m_map.empty(); }
+
+  // lookup
+  std::pair<Key, T> top() const { return *m_map.begin(); }
+
+  // modifiers
+  void pop() { m_map.erase(m_map.begin()); }
+  void push(const Key& key, const T& value) { m_map.emplace(key, value); }
+  void modifyKey(const T& value, const Key& diff) {
+    auto it = std::find_if(m_map.begin(), m_map.end(), [&value](const std::pair<const int, std::string> & p) { return p.second == value; } );
+    Key key = it->first; // take a copy
+    m_map.erase(it);
+    m_map.emplace(key + diff, value);
+  }
+
+private:
+  std::map<Key, T, Compare, Allocator> m_map;
+};
+
+#endif // PRIORITY_QUEUE_HPP