feat: add graph_kruskal

Author: ryukinix

src/graph/Makefile

@@ -14,7 +14,7 @@ INCLUDE := -I../ -L../list/single  -L../hash-table -L../set -L../queue -L../stac
 
 # targets to compile
 TEST_TARGET = test
-TARGETS = graph.o bfs.o dfs.o acyclical.o tarjan.o dijkstra.o
+TARGETS = graph.o bfs.o dfs.o acyclical.o tarjan.o dijkstra.o kruskal.o
 LIBRARY_OBJS = $(TARGETS)
 
 TEST_BINARY = $(TEST_TARGET).$(EXTENSION)

src/graph/graph.h

@@ -273,6 +273,14 @@ List* graph_topological_sort(Graph *g);
  */
 Graph* graph_dijkstra(Graph* g, int source);
 
+/**
+ * @brief Run kruskal algorithm to get the minimum-span tree.
+ * @param g The graph to traverse.
+ * @return a new graph with the minimum span tree.
+ * @ingroup DataStructureMethods
+ */
+Graph* graph_kruskal(Graph* g);
+
 /**
  * @brief Run dijkstra algorithm and calculate the minimum distance.
  * @param g The graph to traverse.

src/graph/kruskal.c

@@ -0,0 +1,24 @@
+#include "graph.h"
+#include "../set/set-disjoint.h"
+
+Graph* graph_kruskal(Graph *g) {
+    Graph *g_kruskal = graph_create();
+    DisjointSet *components = set_disjoint_create(graph_max_node_id(g) + 1);
+    List *edges = graph_edges_ordered(g);
+    Iterator *it = list_iterator(edges);
+
+    while (!iterator_done(it)) {
+        List *edge = (List*) iterator_next(it);
+        int u = edge->key;
+        int v = edge->data;
+        if (set_disjoint_find(components, u) != set_disjoint_find(components, v)) {
+            graph_add_edge_with_weight(g_kruskal, u, v, graph_get_edge_weight(g, u, v));
+            set_disjoint_union(components, u, v);
+        }
+    }
+
+    set_disjoint_free(components);
+    iterator_free(it);
+    list_free(edges);
+    return g_kruskal;
+}

src/graph/test.c

@@ -389,6 +389,27 @@ void test_graph_dijkstra(bool extra_tests) {
     graph_free(dijkstra_result);
 }
 
+void test_graph_kruskal() {
+    puts("== Graph kruskal test");
+    Graph *g = graph_create();
+    graph_add_edge_with_weight(g, 1, 2, 10);
+    graph_add_edge_with_weight(g, 1, 3, 20);
+    graph_add_edge_with_weight(g, 2, 3, 5);
+    graph_add_edge_with_weight(g, 3, 4, 30);
+    graph_add_edge_with_weight(g, 4, 1, 9);
+    graph_add_edge_with_weight(g, 5, 1, 7);
+
+    printf(":: input graph\n");
+    graph_print(g);
+
+    printf(":: kruskal tree\n");
+    Graph *g_kruskal = graph_kruskal(g);
+    graph_print(g_kruskal);
+
+    graph_free(g);
+    graph_free(g_kruskal);
+}
+
 
 bool should_run_extra_tests(int argc, char *argv[]) {
     // Iterate through the command-line arguments starting from argv[1]
@@ -413,6 +434,7 @@ int main(int argc, char *argv[]) {
     test_graph_topological_sort();
     test_graph_dijkstra(extra_tests);
     test_graph_edges_ordered();
+    test_graph_kruskal();
     if (should_run_extra_tests(argc, argv)) {
         test_graph_export();
     }

src/set/set-disjoint.c

@@ -23,16 +23,10 @@ DisjointSet *set_disjoint_create(int n) {
     return ds;
 }
 
-void set_disjoint_destroy(DisjointSet **ds) {
-    if (ds == NULL || *ds == NULL) {
-        return;
-    }
-    free((*ds)->parent);
-    (*ds)->parent = NULL;
-    free((*ds)->rank);
-    (*ds)->rank = NULL;
-    free(*ds);
-    *ds = NULL;
+void set_disjoint_free(DisjointSet *ds) {
+    free(ds->parent);
+    free(ds->rank);
+    free(ds);
 }
 
 // Find with path compression

src/set/set-disjoint.h

@@ -16,11 +16,11 @@ typedef struct DisjointSet DisjointSet;
 DisjointSet *set_disjoint_create(int n);
 
 /**
- * @brief Destroys a disjoint-set data structure.
+ * @brief Free a disjoint-set data structure.
  *
  * @param[in,out] ds A pointer to a pointer to the disjoint-set.
  */
-void set_disjoint_destroy(DisjointSet **ds);
+void set_disjoint_free(DisjointSet *ds);
 
 /**
  * @brief Finds the representative of the set containing element i.

src/set/test.c

@@ -183,8 +183,7 @@ void test_set_disjoint() {
     assert(set_disjoint_find(ds, 8) == set_disjoint_find(ds, 9));
     assert(set_disjoint_find(ds, 0) != set_disjoint_find(ds, 8));
 
-    set_disjoint_destroy(&ds);
-    assert(ds == NULL);
+    set_disjoint_free(ds);
 }