Update app.py

app.py

@@ -102,6 +102,29 @@ def app_hamilton(V, E):
     st.graphviz_chart(G)
 
 
+def solve_vertex_cover(V, E):
+    m = gp.Model()
+    x = m.addVars(range(V), vtype=GRB.BINARY)
+    m.setObjective(x.sum(), GRB.MINIMIZE)
+    m.addConstrs(x[u] + x[v] >= 1 for u, v in E)
+    m.optimize()
+    return [u for u in range(V) if x[u].x > 0.5]
+
+
+def app_vertex_cover(V, E):
+    cover = solve_vertex_cover(V, E)
+    st.metric('Vertex cover size', len(cover))
+    G = graphviz.Graph()
+    for u in range(V):
+        if u in cover:
+            G.node(str(u), style='filled', fillcolor='lightblue')
+        else:
+            G.node(str(u), color='gray')
+    for u, v in E:
+        G.edge(str(u), str(v))
+    st.graphviz_chart(G)
+
+
 def main():
     V = st.number_input('Number of vertices', min_value=1, value=10)
     density = st.slider('Density', min_value=0.0, max_value=1.0, value=0.5)
@@ -113,13 +136,21 @@ def main():
         st.warning('Too many edges to display')
         return
 
-    t1, t2 = st.tabs(['Matching', 'Hamilton'])
-
-    with t1:
-        app_matching(V, E)
-
-    with t2:
-        app_hamilton(V, E)
+    apps = [
+        app_matching,
+        app_hamilton,
+        app_vertex_cover,
+    ]
+
+    tabs = st.tabs([
+        'Matching',
+        'Hamilton',
+        'Vertex cover',
+    ])
+
+    for t, a in zip(tabs, apps):
+        with t:
+            a(V, E)
 
 if __name__ == '__main__':
     main()