From 9c669f2d038012e356202c0a7f16f065f4b684c7 Mon Sep 17 00:00:00 2001
From: Joris van Rantwijk <joris@jorisvr.nl>
Date: Thu, 18 May 2023 09:55:55 +0200
Subject: [PATCH] Remove dependence on Boost.Hash

---
 cpp/mwmatching.h | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/cpp/mwmatching.h b/cpp/mwmatching.h
index 8d05e18..8bc5d45 100644
--- a/cpp/mwmatching.h
+++ b/cpp/mwmatching.h
@@ -1,8 +1,5 @@
 /**
  * Algorithm for finding a maximum weight matching in general graphs.
- *
- * Depends on Boost.Hash.
- * Tested with Boost v1.74, available from https://www.boost.org/
  */
 
 #ifndef MWMATCHING_H_
@@ -18,12 +15,9 @@
 #include <stack>
 #include <stdexcept>
 #include <tuple>
-#include <unordered_set>
 #include <utility>
 #include <vector>
 
-#include <boost/functional/hash.hpp>
-
 
 namespace mwmatching {
 
@@ -95,7 +89,7 @@ inline VertexPair flip_vertex_pair(const VertexPair& vt)
  * The graph may not have self-edges or multiple edges between
  * the same pair of vertices. Edge weights must be within a valid range.
  *
- * This function takes time O(m).
+ * This function takes time O(m * log(m)).
  *
  * @param  edges  Vector of weighted edges defining the graph.
  * @throw  std::invalid_argument  If the input graph is not valid.
@@ -136,16 +130,20 @@ void check_input_graph(const std::vector<Edge<WeightType>>& edges)
     }
 
     // Check that the graph does not contain duplicate edges.
-    std::unordered_set<VertexPair, boost::hash<VertexPair>> edges_seen;
+    std::vector<VertexPair> edge_endpoints;
+    edge_endpoints.reserve(edges.size());
     for (const Edge<WeightType>& edge : edges) {
         VertexPair vt = edge.vt;
         if (vt.first > vt.second) {
-            vt = flip_vertex_pair(vt);
-        }
-        auto status = edges_seen.insert(vt);
-        if (!status.second) {
-            throw std::invalid_argument("Duplicate edges are not supported");
+            std::swap(vt.first, vt.second);
         }
+        edge_endpoints.push_back(vt);
+    }
+
+    std::sort(edge_endpoints.begin(), edge_endpoints.end());
+    if (std::unique(edge_endpoints.begin(), edge_endpoints.end())
+            != edge_endpoints.end()) {
+        throw std::invalid_argument("Duplicate edges are not supported");
     }
 }