From 523c27294c16004e65154f26fe411dc5f8ee0579 Mon Sep 17 00:00:00 2001
From: Pulkit Mishra <pulkitmishra007@gmail.com>
Date: Tue, 29 Oct 2019 03:38:18 +0530
Subject: [PATCH] Adds Floyd Warshall Algorithm

---
 graphing/floyd_warshall.py | 142 +++++++++++++++++++++++++++++++++++++
 1 file changed, 142 insertions(+)
 create mode 100644 graphing/floyd_warshall.py

diff --git a/graphing/floyd_warshall.py b/graphing/floyd_warshall.py
new file mode 100644
index 0000000..bae93d8
--- /dev/null
+++ b/graphing/floyd_warshall.py
@@ -0,0 +1,142 @@
+class Graph:
+    def __init__(self):
+        self.vertices = {}
+ 
+    def add_vertex(self, key):
+        vertex = Vertex(key)
+        self.vertices[key] = vertex
+ 
+    def get_vertex(self, key):
+        return self.vertices[key]
+ 
+    def __contains__(self, key):
+        return key in self.vertices
+ 
+    def add_edge(self, src_key, dest_key, weight=1):
+        self.vertices[src_key].add_neighbour(self.vertices[dest_key], weight)
+ 
+    def does_edge_exist(self, src_key, dest_key):
+        return self.vertices[src_key].does_it_point_to(self.vertices[dest_key])
+ 
+    def __len__(self):
+        return len(self.vertices)
+ 
+    def __iter__(self):
+        return iter(self.vertices.values())
+ 
+ 
+class Vertex:
+    def __init__(self, key):
+        self.key = key
+        self.points_to = {}
+ 
+    def get_key(self):
+        return self.key
+ 
+    def add_neighbour(self, dest, weight):
+        self.points_to[dest] = weight
+ 
+    def get_neighbours(self):
+        return self.points_to.keys()
+ 
+    def get_weight(self, dest):
+        return self.points_to[dest]
+ 
+    def does_it_point_to(self, dest):
+        return dest in self.points_to
+ 
+ 
+def floyd_warshall(g):
+    distance = {v:dict.fromkeys(g, float('inf')) for v in g}
+    next_v = {v:dict.fromkeys(g, None) for v in g}
+ 
+    for v in g:
+        for n in v.get_neighbours():
+            distance[v][n] = v.get_weight(n)
+            next_v[v][n] = n
+ 
+    for v in g:
+         distance[v][v] = 0
+         next_v[v][v] = None
+ 
+    for p in g: 
+        for v in g:
+            for w in g:
+                if distance[v][w] > distance[v][p] + distance[p][w]:
+                    distance[v][w] = distance[v][p] + distance[p][w]
+                    next_v[v][w] = next_v[v][p]
+ 
+    return distance, next_v
+ 
+ 
+def print_path(next_v, u, v):
+    
+    p = u
+    while (next_v[p][v]):
+        print('{} -> '.format(p.get_key()), end='')
+        p = next_v[p][v]
+    print('{} '.format(v.get_key()), end='')
+ 
+ 
+g = Graph()
+print('Menu')
+print('add vertex <key>')
+print('add edge <src> <dest> <weight>')
+print('floyd-warshall')
+print('display')
+print('quit')
+ 
+while True:
+    do = input('What would you like to do? ').split()
+ 
+    operation = do[0]
+    if operation == 'add':
+        suboperation = do[1]
+        if suboperation == 'vertex':
+            key = int(do[2])
+            if key not in g:
+                g.add_vertex(key)
+            else:
+                print('Vertex already exists.')
+        elif suboperation == 'edge':
+            src = int(do[2])
+            dest = int(do[3])
+            weight = int(do[4])
+            if src not in g:
+                print('Vertex {} does not exist.'.format(src))
+            elif dest not in g:
+                print('Vertex {} does not exist.'.format(dest))
+            else:
+                if not g.does_edge_exist(src, dest):
+                    g.add_edge(src, dest, weight)
+                else:
+                    print('Edge already exists.')
+ 
+    elif operation == 'floyd-warshall':
+        distance, next_v = floyd_warshall(g)
+        print('Shortest distances:')
+        for start in g:
+            for end in g:
+                if next_v[start][end]:
+                    print('From {} to {}: '.format(start.get_key(),
+                                                    end.get_key()),
+                            end = '')
+                    print_path(next_v, start, end)
+                    print('(distance {})'.format(distance[start][end]))
+ 
+    elif operation == 'display':
+        print('Vertices: ', end='')
+        for v in g:
+            print(v.get_key(), end=' ')
+        print()
+ 
+        print('Edges: ')
+        for v in g:
+            for dest in v.get_neighbours():
+                w = v.get_weight(dest)
+                print('(src={}, dest={}, weight={}) '.format(v.get_key(),
+                                                             dest.get_key(), w))
+        print()
+ 
+    elif operation == 'quit':
+        break