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Some help needed for SPOJ Matching problem

Revision en1, by mranjan7, 2021-09-03 06:45:38

I am getting TLE for following problem : http://www.spoj.com/problems/MATCHING/ . I have used Hopcroft–Karp algorithm :

import java.util.*;
public class MatchingHK{
    static int N;
    static int M;
    static int P;
    static int pairU[];
    static int pairV[];
    static int dist[];
    static int NIL = 0;
    static int INF = Integer.MAX_VALUE;
    static ArrayList<Integer> adj[];

    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        N = sc.nextInt();
        M = sc.nextInt();
        P = sc.nextInt();
        pairU = new int[N+1];
        pairV = new int[M+1];
        dist = new int[N+1];
        adj = new ArrayList[N+1];
        for(int i = 1;i <= N;i++){
            adj[i] = new ArrayList<Integer>();
        }
        for(int i = 0;i < P;i++){
            int c = sc.nextInt();
            int b = sc.nextInt();
            adj[c].add(b);
        }
        System.out.println(maxMatching());
    }
    public static int maxMatching(){
        int result = 0;
        
        while(bfs()){
            for(int i = 1;i <= N;i++){
                if(pairU[i] == NIL && dfs(i)){
                    result++;
                }
            }
        }

        return result;
    }

    public static boolean bfs(){
        PriorityQueue<Integer> q = new PriorityQueue<Integer>();
        for(int i = 1;i <= N;i++){
            if(pairU[i] == NIL){
                dist[i] = 0;
                q.add(i);
            }
            else{
                dist[i] = INF;
            }
        }
        dist[NIL] = INF;
        while(!q.isEmpty()){
            int u = q.poll();
            if(dist[u] < dist[NIL]){
                for(int v : adj[u]){
                    if(dist[pairV[v]] == INF){
                        dist[pairV[v]] = dist[u] + 1;
                        q.offer(pairV[v]);
                    }
                }
            }
        }
        return (dist[NIL] != INF);
    }

    public static boolean dfs(int u){
        if(u != NIL){
            for(int v : adj[u]){
                if(dist[pairV[v]] == (dist[u]+1) && dfs(pairV[v])){
                    pairV[v] = u;
                    pairU[u] = v;
                    return true;
                } 
            }
            dist[u] = INF;
            return false;
            
        }
        return true;
    }
}

Is my implementation of Hopcroft Karp algorithm wrong or do I need to use different algorithm for above problem?

Tags #algorithms, #bipartite, #spoj, #graph

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en1 English mranjan7 2021-09-03 06:45:38 2617 Initial revision (published)