Merge pull request #94 from CSRT-NTUA/spiros-dev

Added scc function on weighted graph
CSRT-NTUA · Nov 28, 2024 · aa4d393 · aa4d393
2 parents 40e6b88 + 6074251
commit aa4d393
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diff --git a/src/classes/graph/graph.h b/src/classes/graph/graph.h
@@ -507,7 +507,7 @@ template <typename T> int64_t graph<T>::scc() {
 
     std::unordered_map<T, std::vector<T> > new_adj;
     for(const T& x: _elements) {
-        for(auto & neigh: adj[x]) {
+        for(const auto& neigh: adj[x]) {
             new_adj[neigh].push_back(x);
         }
     }
@@ -866,6 +866,20 @@ template <typename T> class weighted_graph {
       }
     }
   }
+
+  /**
+  * @brief helper dfs function for kosaraju's scc
+  */
+  void dfs_scc(T start, std::unordered_map<T, bool> &visited, std::stack<T> &s) {
+      visited[start] = true;
+      for(auto & x : adj[start]) {
+          if(visited.find(x.first) == visited.end()) {
+              dfs_scc(x.first, visited, s);
+          }
+      }
+
+      s.push(start);
+  }
 };
 
 template <typename T> size_t weighted_graph<T>::size() {
@@ -1144,6 +1158,59 @@ std::vector<std::vector<T>> weighted_graph<T>::bridge(T start) {
   return bridges;
 }
 
+template <typename T>
+int64_t weighted_graph<T>::scc() {
+    if (this -> size() == 0) {
+        return 0;
+    }
+
+    std::unordered_map<T, bool> visited;
+    std::stack<T> s;
+
+    for(const T& x : _elements) {
+        if(visited.find(x) == visited.end()) {
+            dfs_scc(x, visited, s);
+        }
+    }
+
+    std::unordered_map<T, std::vector<T> > new_adj;
+    for(const T& x: _elements) {
+        for(const auto& neigh: adj[x]) {
+            new_adj[neigh.first].push_back(x);
+        }
+    }
+
+    int64_t scc = 0;
+    visited.clear();
+
+    auto dfs_new = [&](T start) -> void {
+        std::stack<T> _s;
+        _s.push(start);
+        visited[start] = true;
+        while(!_s.empty()) {
+            T current = _s.top();
+            _s.pop();
+            for(auto & x: new_adj[current]) {
+                if (visited.find(x) == visited.end()) {
+                    _s.push(x);
+                    visited[x] = true;
+                }
+            }
+        }
+    };
+
+    while(!s.empty()) {
+        T current = s.top();
+        s.pop();
+        if (visited.find(current) == visited.end()) {
+            dfs_new(current);
+            scc++;
+        }
+    }
+
+    return scc;
+}
+
 template <typename T> bool weighted_graph<T>::connected() {
   std::unordered_map<T, bool> visited;
   bool check = 0;

diff --git a/tests/graph/weighted_graph.cc b/tests/graph/weighted_graph.cc
@@ -296,6 +296,57 @@ TEST_CASE("Testing shortest path algorithm [2]") {
     REQUIRE(g.shortest_path(1, 7) == 56);
 }
 
+TEST_CASE("Testing scc function for weighted graph class") {
+    weighted_graph<int> g("directed");
+    g.add_edge(0, 1, 50);
+    g.add_edge(1, 2, 50);
+    g.add_edge(2, 0, 50);
+    g.add_edge(1, 3, 50);
+    g.add_edge(3, 4, 50);
+    g.add_edge(4, 3, 50);
+
+    REQUIRE(g.scc() == 2);
+
+    weighted_graph<int> g2("undirected");
+    REQUIRE(g2.scc() == 0);
+
+    g2.add_edge(0, 1, 5);
+    g2.add_edge(1, 2, 5);
+    g2.add_edge(2, 0, 5);
+    g2.add_edge(3, 4, 5);
+    g2.add_edge(4, 5, 5);
+    g2.add_edge(5, 3, 5);
+    g2.add_edge(3, 6, 5);
+    g2.add_edge(1, 3, 5);
+
+    REQUIRE(g2.scc() == 1);
+
+    weighted_graph<char> t("directed");
+    t.add_edge('a', 'b', 5);
+    t.add_edge('b', 'c', 5);
+    t.add_edge('c', 'a', 5);
+    t.add_edge('b', 'd', 5);
+    t.add_edge('d', 'e', 5);
+    t.add_edge('e', 'd', 5);
+
+    REQUIRE(t.scc() == 2);
+
+    weighted_graph<int> g3("directed");
+    g3.add_edge(0, 1, 5);
+    g3.add_edge(1, 2, 5);
+    g3.add_edge(2, 0, 5);
+    g3.add_edge(1, 3, 5);
+    g3.add_edge(3, 4, 5);
+    g3.add_edge(4, 5, 5);
+    g3.add_edge(5, 3, 5);
+    g3.add_edge(3, 6, 5);
+    g3.add_edge(6, 7, 5);
+    g3.add_edge(6, 8, 5);
+    g3.add_edge(8, 6, 5);
+
+    REQUIRE(g3.scc() == 4);
+}
+
 #define GRAPH_VISUALIZATION_H
 
 #ifdef GRAPH_VISUALIZATION_H