From 55985ab0092b2eee94879ab6d465c9d0609730cd Mon Sep 17 00:00:00 2001
From: may55 <mayank.soni055@gmail.com>
Date: Thu, 3 Oct 2019 02:04:55 +0530
Subject: [PATCH] Added Dijkstra.py

---
 .../Single_Source_Shortest_Path/Dijkstra.py   | 59 +++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 Graph_Algorithms/src/Single_Source_Shortest_Path/Dijkstra.py

diff --git a/Graph_Algorithms/src/Single_Source_Shortest_Path/Dijkstra.py b/Graph_Algorithms/src/Single_Source_Shortest_Path/Dijkstra.py
new file mode 100644
index 00000000..9fe3cd13
--- /dev/null
+++ b/Graph_Algorithms/src/Single_Source_Shortest_Path/Dijkstra.py
@@ -0,0 +1,59 @@
+
+def dijkstra(graph, s, v):
+    ##priority is set first so that pop is easy 
+    ##min/max by default is based on the first element of tuple when we have a list of tuples
+    pq_dist = [(float("Inf"), i) for i in range(v)]
+    ##set source pq= 0
+    pq_dist[s] =  (0, s)
+    v = len(graph)
+    
+    ##create ix and dist list
+    done_dist = []
+    done_ix = []
+    for vertex in range(v):
+        ###deque frpm pq
+        dq_ele = pq_dist.pop(pq_dist.index(min(pq_dist)))
+        dq_ix = dq_ele[1]
+        
+        ##add to done
+        done_dist.append(dq_ele[0])
+        done_ix.append(dq_ele[1])
+
+        
+        #get the neighbours pf rem ele not in done
+        neighbours = [i for i in range(len(graph[dq_ix])) if graph[dq_ix][i] != 0 and 
+                    i not in done_ix]
+        
+        ##update dist of neigh in pq
+        #add neigh to pq
+        if len(neighbours) > 0:
+            ##iternate through all un-finalized neighbours
+            for n in neighbours:
+                if len(pq_dist) > 1:
+                    ##we can use zip
+                    ix_of_n_in_pq = list(list(zip(*tuple(pq_dist)))[1]).index(n)
+                else:
+                    ##we cannot use zip so default 0
+                    ix_of_n_in_pq = 0
+                ##if old priority > new_priority, update
+                if len(pq_dist) > 0 and pq_dist[ix_of_n_in_pq][0] > dq_ele[0] + graph[dq_ix][n]:
+                    pq_dist[ix_of_n_in_pq] = (dq_ele[0] + graph[dq_ix][n], n)
+        else:
+            ##no new neighbours found
+            break
+    ##get the index that will sort the vertices
+    ##rectified the input as range(len(done_ix))
+    sorted_ix = sorted(range(len(done_ix)), key=lambda k: done_ix[k])
+    
+    ##ouput dist in the order of vertices
+    output = [done_dist[d] for d in sorted_ix]#list(list(zip(*tuple(done_list)))[1])
+    print (" ".join([str(e) for e in output]), end = "")
+
+if __name__ == '__main__':
+    
+    adjacency_matrix  = [[0,1,43],[1,0,6],[43,6,0]]
+
+    # this function will print shortest path of source to all the vertices.
+    src = 2
+    number_of_vertices = 3
+    dijkstra(adjacency_matrix,src, number_of_vertices)