Merge pull request #174 from bettoarcaya/adding-dijkstra-algorithm

Adding dijkstra algorithm

Author: ionicc

Graph_Algorithms/src/Dijkstra/Dijkstra.py

@@ -0,0 +1,68 @@
+from collections import defaultdict
+import math
+
+class Graph:
+  def __init__(self):
+    self.nodes = set()
+    self.archs = defaultdict(list)
+    self.values = {}
+
+  def add_node(self, value):
+    self.nodes.add(value)
+
+  def add_edge(self, init_node, final_node, value):
+    self.archs[init_node].append(final_node)
+    self.archs[init_node].append(final_node)
+    self.values[(init_node, final_node)] = value
+
+
+def dijkstra(graph, initial):
+  visited = {initial: 0}
+
+  nodes = set(graph.nodes)
+
+  while nodes:
+    min_node = None
+    for node in nodes:
+      if node in visited:
+        if min_node is None:
+          min_node = node
+        elif visited[node] < visited[min_node]:
+          min_node = node
+
+    if min_node is None:
+      break
+
+    nodes.remove(min_node)
+    current_weight = visited[min_node]
+
+    for arch in graph.archs[min_node]:
+      try:
+          weight = current_weight + graph.values[(min_node, arch)]
+      except:
+          weight = current_weight + math.inf
+      if arch not in visited or weight < visited[arch]:
+        visited[arch] = weight
+
+  return visited
+
+
+def main():
+
+    #initializing values
+    g = Graph()
+    g.add_node('a')
+    g.add_node('b')
+    g.add_node('c')
+    g.add_node('d')
+
+    g.add_edge('a', 'b', 10)
+    g.add_edge('b', 'c', 2)
+    g.add_edge('a', 'c', 1)
+    g.add_edge('c', 'd', 1)
+    g.add_edge('b', 'd', 8)
+
+    #output
+    print(dijkstra(g, 'a'))
+
+main()