From c6567116253fa74f119aaeffa01ae5283e046c66 Mon Sep 17 00:00:00 2001
From: Valentin Gehrke <madmaurice@zom.bi>
Date: Wed, 10 Feb 2016 18:07:36 +0100
Subject: [PATCH] Added prim algorithm

---
 graph.py | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/graph.py b/graph.py
index 06bc21d..acc6230 100644
--- a/graph.py
+++ b/graph.py
@@ -83,6 +83,28 @@ def dfs(graph, node, visited=None):
             for node in dfs(graph, neighbor, visited=visited):
                 yield node
 
+def prim(graph,r=None):
+    if r is None:
+        r = list(graph.nodes)[0]
+    Vt = set();
+    Vt.add(r);
+    d = { node: Infinity() for node in graph.nodes }
+    d[r] = 0;
+    for _, neighbor, distance in graph.all_edges_of(r):
+        d[neighbor] = distance
+
+    while Vt < graph.nodes:
+        u = min(graph.nodes - Vt, key=lambda node: d[node])
+        if d[u] == Infinity():
+            break
+        Vt.add(u)
+        for _, neighbor, distance in graph.all_edges_of(u):
+            if neighbor not in Vt:
+                d[neighbor] = min([ d[neighbor], distance ])
+
+    return d;
+
+
 def main():
     g = Graph()
     for i in range(1,6):
@@ -100,6 +122,10 @@ def main():
 
     print(d)
 
+    d = prim(g)
+
+    print(d)
+
     print( list(bfs(g,1)) )
     print( list(dfs(g,1)) )
 
@@ -114,6 +140,26 @@ def main():
     print( list(bfs(g2,1)) )
     print( list(dfs(g2,1)) )
 
+    g3 = Graph()
+    g3.add_node(1)
+    g3.add_node(2)
+    g3.add_node(3)
+    g3.add_node(4)
+    g3.add_node(5)
+    g3.add_node(6)
+
+    g3.add_edge(1,2,20)
+    g3.add_edge(1,3,10)
+    g3.add_edge(2,4,30)
+    g3.add_edge(2,5,20)
+    g3.add_edge(3,4,10)
+    g3.add_edge(3,5,20)
+    g3.add_edge(4,6,10)
+    g3.add_edge(5,6,30)
+
+    d = prim(g3,1)
+    print(d)
+
 
 
 if __name__ == '__main__':