addtition: graph veretx count and get veretx

include/graph.h

@@ -30,7 +30,7 @@ GraphErr graph_connect_vertex(
     size_t node2,
     size_t weight);
 
-GraphErr graph_vertex_count(size_t *out);
+GraphErr graph_vertex_count(Graph *graph, size_t *out);
 GraphErr graph_get_vertex(Graph *graph, size_t index, Vertex *out);
 
 #endif

src/graph.c

@@ -98,3 +98,27 @@ GraphErr graph_connect_vertex(
 
     return GRAPH_OK;
 }
+
+GraphErr graph_vertex_count(Graph *graph, size_t *out) {
+    if (graph == NULL) {
+        return GRAPH_NULL_ARG;
+    }
+
+    *out = arraylist_size(graph->vertices);
+
+    return GRAPH_OK;
+}
+
+GraphErr graph_get_vertex(Graph *graph, size_t index, Vertex *out) {
+    if (graph == NULL || out == NULL) {
+        return GRAPH_NULL_ARG;
+    }
+
+    if (index >= arraylist_size(graph->vertices)) {
+        return GRAPH_VERTEX_NOT_FOUND;
+    }
+
+    arraylist_get(graph->vertices, index, out);
+
+    return GRAPH_OK;
+}