(UVA) IP-TV - Solution 1

I used Prim's algorithm to solve this problem.


import java.io.*;
import java.util.*;

class Main  {
    public static HashMap<String, ArrayList<Edge>> adjList;
   
    public static Comparator<Edge> costComparator = new Comparator<Edge>() {
        public int compare(Edge e1, Edge e2) {
            return e1.cost-e2.cost;
        }
    };
   
    public static int prim(String start, int numCities) {
        Queue<Edge> queue = new PriorityQueue<Edge>(numCities, costComparator);
        queue.add(new Edge(start, 0));
       
        HashSet<String> visited = new HashSet<String>();
       
        int totalCost = 0;
        while (queue.size() > 0) {
            Edge curr = queue.poll();
            String currCity = curr.city;
            int currCost = curr.cost;
           
            if (visited.contains(currCity)) {
                continue;
            }
            visited.add(currCity);
           
            totalCost += currCost;
            if (visited.size() == numCities) {
                return totalCost;
            }
           
            ArrayList<Edge> reachCities = adjList.get(currCity);
            for (int i = 0; i < reachCities.size(); i++) {
                queue.add(reachCities.get(i));
            }
        }
       
        return -1;
    }
   
    public static int reader(BufferedReader br) throws NumberFormatException, IOException {     
        int n;
        int resp = 0;     
      
        while (true) {         
            n = br.read();         
            if (n >= '0' && n <= '9') {
                break;
            }
        }
           
        while (true) {         
            resp = resp*10 + n-'0';         
            n = br.read();         
            if (n < '0' || n > '9') {
                break;     
            }
        }
      
        return resp;     
    }
   
    public static void process() throws NumberFormatException, IOException {  
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
       
        int numTests = reader(br);
        for (int i = 0; i < numTests; i++) {
            if (i > 0) {
                System.out.println();
            }
           
            int numCities = reader(br);
            int numLinks = reader(br);
           
            String cityStart = "";
            adjList = new HashMap<String, ArrayList<Edge>>();
            for (int j = 0; j < numLinks; j++) {
                String line = br.readLine();
                String[] s = line.split("\\s");
               
                String city1 = s[0];
                String city2 = s[1];
                int cost = Integer.parseInt(s[2]);
               
                if (!adjList.containsKey(city1)) {
                    adjList.put(city1, new ArrayList<Edge>());
                }
                if (!adjList.containsKey(city2)) {
                    adjList.put(city2, new ArrayList<Edge>());
                }
                adjList.get(city1).add(new Edge(city2, cost));
                adjList.get(city2).add(new Edge(city1, cost));
               
                cityStart = city1;
            }
           
            System.out.println(prim(cityStart, numCities));
        }
               
        return;
    }
  
    public static void main(String[] args) throws NumberFormatException, IOException {
        Main m = new Main();
        m.process();

        System.exit(0);
    }
}

class Edge {
    String city;
    int cost;
   
    public Edge(String city, int cost) {
        this.city = city;
        this.cost = cost;
    }
}