Added few more comments.

Author: Navjinder Virdee

Contraction Hierarchies/DistPreprocessSmall.java

@@ -1,4 +1,4 @@
-//Program to implement Contraction Hierarchies Algorithm
+//Program to implement Contraction Hierarchies Algorithm.
 
 import java.util.Scanner;
 import java.util.ArrayList;
@@ -38,7 +38,7 @@ public Distance(){
 }
  }
 
- //in this ids are made for the same reason, to not have to reinitialize processed variable. for every query in bidirectional dijkstra.
+ //in this ids are made for the same reason, to not have to reinitialize processed variable for every query in bidirectional dijkstra.
  static class Processed{
 boolean forwProcessed; //is processed in forward search.
 boolean revProcessed; //is processed in backward search.
@@ -51,7 +51,7 @@ public Processed(){
 }
  }
 
- //class for Vertex
+ //class for Vertex of a graph.
  static class Vertex{
 int vertexNum;//id of the vertex.
 ArrayList<Integer> inEdges; //list of incoming edges to this vertex.
@@ -66,10 +66,10 @@ static class Vertex{
 Distance distance;
 Processed processed;
 
-//parameters for computing importance.
-int edgeDiff; //egdediff = sE - inE - outE.
-long delNeighbors; // number of contracted neighbors.
-int shortcutCover; // number of shotcuts to be introduces if this vertex is contracted.
+//parameters for computing importance according to which we will contract the vertices. Vertex wih least importance wil be contracted first.
+int edgeDiff; //egdediff = sE - inE - outE. (sE=inE*outE , i.e number of shortcuts that we may have to add.)
+long delNeighbors; //number of contracted neighbors.
+int shortcutCover; //number of shortcuts to be introduced if this vertex is contracted.
 
 long importance; //total importance = edgediff + shortcutcover + delneighbors.
 
@@ -155,8 +155,9 @@ private void computeImportance(Vertex [] graph, Vertex vertex){
 
 while(PQImp.size()!=0){
 Vertex vertex = (Vertex)PQImp.poll();
-computeImportance(graph,vertex);//recompute importance before contractingthe vertex.
+computeImportance(graph,vertex);//recompute importance before contracting the vertex.
 
+//if the vertex's recomputed importance is still minimum then contract it.
 if(PQImp.size()!=0 && vertex.importance > PQImp.peek().importance){
 PQImp.add(vertex);
 continue;
@@ -166,13 +167,14 @@ private void computeImportance(Vertex [] graph, Vertex vertex){
 vertex.orderPos = extractNum; 
 extractNum = extractNum + 1;
 
-contractNode(graph,vertex,extractNum-1);//contraction part.
+//contraction part.
+contractNode(graph,vertex,extractNum-1);
 }
 return nodeOrdering;
 }
 
 
-//update the neighbors of the contracted vertex that this this vertex is contracted.
+//update the neighbors of the contracted vertex that this vertex is contracted.
 private void calNeighbors(Vertex [] graph,ArrayList<Integer> inEdges, ArrayList<Integer> outEdges){
 for(int i=0;i<inEdges.size();i++){
 int temp =inEdges.get(i);
@@ -218,7 +220,7 @@ private void contractNode(Vertex [] graph, Vertex vertex, int contractId){
 }
 }
 
-long max = inMax+outMax; //total max distance.
+long max = inMax+outMax; //total max distance.
 
 for(int i=0;i<inEdges.size();i++){
 int inVertex = inEdges.get(i);
@@ -300,7 +302,7 @@ private boolean checkId(Vertex [] graph,int source,int target){
 
 //main function of this class.
 public int [] processing(Vertex [] graph){
-computeImportance(graph);//find initial importance by traversing all vertices.
+computeImportance(graph);//find initial importance by traversing all vertices.
 int [] nodeOrdering = preProcess(graph);
 return nodeOrdering;
 }
@@ -491,4 +493,4 @@ public static void main(String args[]) {
  System.out.println(bd.computeDist(graph,u,v,i,nodeOrdering));
  }
  }
-}
+}