Added page-rank algorithm implementation (TheAlgorithms#780)

* Added page-rank algorithm implementation

* changed init variables

Author: bhushan-borole

Diff for: Graphs/pagerank.py

@@ -0,0 +1,72 @@
+'''
+Author: https://github.com/bhushan-borole
+'''
+'''
+The input graph for the algorithm is:
+
+  A B C
+A 0 1 1
+B 0 0 1
+C 1 0 0
+
+'''
+
+graph = [[0, 1, 1],
+    	[0, 0, 1],
+    	[1, 0, 0]]
+
+
+class Node:
+    def __init__(self, name):
+        self.name = name
+        self.inbound = []
+        self.outbound = []
+    
+    def add_inbound(self, node):
+        self.inbound.append(node)
+    
+    def add_outbound(self, node):
+        self.outbound.append(node)
+    
+    def __repr__(self):
+        return 'Node {}: Inbound: {} ; Outbound: {}'.format(self.name,
+                                                      	self.inbound,
+                                                      	self.outbound)
+
+
+def page_rank(nodes, limit=3, d=0.85):
+    ranks = {}
+    for node in nodes:
+        ranks[node.name] = 1
+
+    outbounds = {}
+    for node in nodes:
+        outbounds[node.name] = len(node.outbound)
+
+    for i in range(limit):
+        print("======= Iteration {} =======".format(i+1))
+        for j, node in enumerate(nodes):
+            ranks[node.name] = (1 - d) + d * sum([ ranks[ib]/outbounds[ib] for ib in node.inbound ])
+        print(ranks)
+
+
+def main():
+    names = list(input('Enter Names of the Nodes: ').split())
+
+    nodes = [Node(name) for name in names]
+    
+    for ri, row in enumerate(graph):
+        for ci, col in enumerate(row):
+            if col == 1:
+                nodes[ci].add_inbound(names[ri])
+                nodes[ri].add_outbound(names[ci])
+
+    print("======= Nodes =======")
+    for node in nodes:
+        print(node)
+
+    page_rank(nodes)
+
+
+if __name__ == '__main__':
+    main()