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‎Graphs/.ipynb_checkpoints/Implementation of Adjacency List-checkpoint.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Implementation of a Graph as an Adjacency List\n",
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"\n",
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"\n",
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"Using dictionaries, it is easy to implement the adjacency list in Python. In our implementation of the Graph abstract data type we will create two classes: **Graph**, which holds the master list of vertices, and **Vertex**, which will represent each vertex in the graph.\n",
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"\n",
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"Each Vertex uses a dictionary to keep track of the vertices to which it is connected, and the weight of each edge. This dictionary is called **connectedTo**. The constructor simply initializes the id, which will typically be a string, and the **connectedTo** dictionary. The **addNeighbor** method is used add a connection from this vertex to another. The **getConnections** method returns all of the vertices in the adjacency list, as represented by the **connectedTo** instance variable. The **getWeight** method returns the weight of the edge from this vertex to the vertex passed as a parameter."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"execution_count": 3,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": []
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"source": [
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"class Vertex:\n",
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" def __init__(self,key):\n",
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" self.id = key\n",
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" self.connectedTo = {}\n",
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"\n",
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" def addNeighbor(self,nbr,weight=0):\n",
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" self.connectedTo[nbr] = weight\n",
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"\n",
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" def __str__(self):\n",
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" return str(self.id) + ' connectedTo: ' + str([x.id for x in self.connectedTo])\n",
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"\n",
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" def getConnections(self):\n",
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" return self.connectedTo.keys()\n",
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"\n",
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" def getId(self):\n",
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" return self.id\n",
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"\n",
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" def getWeight(self,nbr):\n",
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" return self.connectedTo[nbr]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {
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"collapsed": true
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},
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"source": [
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"In order to implement a Graph as an Adjacency List what we need to do is define the methods our Adjacency List object will have:\n",
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"\n",
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"* **Graph()** creates a new, empty graph.\n",
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"* **addVertex(vert)** adds an instance of Vertex to the graph.\n",
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"* **addEdge(fromVert, toVert)** Adds a new, directed edge to the graph that connects two vertices.\n",
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"* **addEdge(fromVert, toVert, weight)** Adds a new, weighted, directed edge to the graph that connects two vertices.\n",
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"* **getVertex(vertKey)** finds the vertex in the graph named vertKey.\n",
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"* **getVertices()** returns the list of all vertices in the graph. \n",
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"* **in** returns True for a statement of the form vertex in graph, if the given vertex is in the graph, False otherwise."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 4,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"class Graph:\n",
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" def __init__(self):\n",
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" self.vertList = {}\n",
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" self.numVertices = 0\n",
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"\n",
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" def addVertex(self,key):\n",
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" self.numVertices = self.numVertices + 1\n",
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" newVertex = Vertex(key)\n",
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" self.vertList[key] = newVertex\n",
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" return newVertex\n",
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"\n",
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" def getVertex(self,n):\n",
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" if n in self.vertList:\n",
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" return self.vertList[n]\n",
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" else:\n",
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" return None\n",
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"\n",
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" def __contains__(self,n):\n",
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" return n in self.vertList\n",
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"\n",
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" def addEdge(self,f,t,cost=0):\n",
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" if f not in self.vertList:\n",
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" nv = self.addVertex(f)\n",
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" if t not in self.vertList:\n",
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" nv = self.addVertex(t)\n",
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" self.vertList[f].addNeighbor(self.vertList[t], cost)\n",
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"\n",
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" def getVertices(self):\n",
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" return self.vertList.keys()\n",
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"\n",
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" def __iter__(self):\n",
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" return iter(self.vertList.values())"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Let's see a simple example of how to use this:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 5,
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"metadata": {
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"collapsed": false
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},
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"outputs": [],
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"source": [
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"g = Graph()\n",
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"for i in range(6):\n",
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" g.addVertex(i)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 6,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"{0: <__main__.Vertex instance at 0x10476b680>,\n",
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" 1: <__main__.Vertex instance at 0x104cce5f0>,\n",
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" 2: <__main__.Vertex instance at 0x10395d950>,\n",
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" 3: <__main__.Vertex instance at 0x1039c00e0>,\n",
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" 4: <__main__.Vertex instance at 0x1039c4e60>,\n",
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" 5: <__main__.Vertex instance at 0x1039c45f0>}"
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]
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},
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"execution_count": 6,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"g.vertList"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 7,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"g.addEdge(0,1,2)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 12,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"0 connectedTo: [1]\n",
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"[<__main__.Vertex instance at 0x104cce5f0>]\n",
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"\n",
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"\n",
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"1 connectedTo: []\n",
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"[]\n",
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"\n",
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"\n",
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"2 connectedTo: []\n",
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"[]\n",
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"\n",
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"\n",
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"3 connectedTo: []\n",
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"[]\n",
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"\n",
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"\n",
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"4 connectedTo: []\n",
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"[]\n",
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"\n",
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"\n",
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"5 connectedTo: []\n",
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"[]\n",
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"\n",
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"\n"
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]
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}
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],
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"source": [
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"for vertex in g:\n",
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" print vertex\n",
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" print vertex.getConnections()\n",
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" print '\\n'"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Great Job!"
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]
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}
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],
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"metadata": {

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