Create floyd_warshall.py

Author: careermonk

dynamic-programming/floyd_warshall.py

@@ -0,0 +1,52 @@
+# Copyright (c) June 02, 2017 CareerMonk Publications and others.
+# E-Mail           		: [email protected]
+# Creation Date    		: 2017-06-02 06:15:46
+# Last modification		: 2017-06-02
+# Modified by		        : Narasimha Karumanchi
+# Book Title			: Algorithm Design Techniques
+# Warranty         		: This software is provided "as is" without any
+# 				 warranty; without even the implied warranty of
+# 				 merchantability or fitness for a particular purpose.
+
+def adj(graph):
+    vertices = graph.keys()
+ 
+    D = {}
+    for i in vertices:
+        D[i] = {}
+        for j in vertices:
+            try:
+                D[i][j] = graph[i][j]
+            except KeyError:
+                # the distance from a node to itself is 0
+                if i == j:
+                    D[i][j] = 0
+                    # the distance from a node to an unconnected node is infinity
+                else:
+                    D[i][j] = float('inf')
+    return D
+
+def floyd_warshall(graph):
+    vertices = graph.keys()
+ 
+    d = dict(graph) # copy graph
+    for k in vertices:
+        for i in vertices:
+            for j in vertices:
+                d[i][j] = min(d[i][j], d[i][k] + d[k][j])
+    return d
+ 
+
+if __name__ == "__main__":
+    graph = {'c': {'a':5, 'b':2, 'd':1, 'h':2},
+                'a': {'b':3, 'c':5, 'e':8, 'f':1},
+                'b': {'a':3, 'c':2, 'g':1},            
+                'd': {'c':1, 'e':4},
+                'e': {'a':8, 'd':4, 'f':6, 'h':1},
+                'f': {'a':1, 'e':6, 'g':5},
+                'g': {'b':1, 'f':5, 'h':1},
+                'h': {'c':2, 'e':1, 'g':1}}
+    matrix=adj(graph)
+    print     matrix
+    print floyd_warshall(matrix)
+