Example: Circular Dependency Detector - rFronteddu/general_wiki GitHub Wiki

import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.function.*;
import java.util.regex.*;
import java.util.stream.*;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;



class Result {

    /*
     * Complete the 'hasCircularDependency' function below.
     *
     * The function is expected to return a BOOLEAN.
     * The function accepts following parameters:
     *  1. INTEGER n
     *  2. 2D_INTEGER_ARRAY dependencies
     */

    public static boolean dfs(int s, boolean[] visited, boolean[] inStack, List<List<Integer>> g) {
        if(inStack[s]) return true;
        if(visited[s]) return false;
        
        visited[s] = true;
        inStack[s] = true;
        
        for(var n : g.get(s)) {
            if(dfs(n, visited, inStack, g)) return true;
        }
        
        // backtrack
        inStack[s] = false;
        return false;
    }


    public static boolean hasCircularDependency(int n, List<List<Integer>> dependencies) {
        // convert into dep graph
        List<List<Integer>> g = new ArrayList<>();
        for (int i = 0; i < n; i++) g.add(new ArrayList<>());
        for (var link : dependencies) {
            int a = link.get(0); int b = link.get(1);
            g.get(a).add(b);
        }
        
        if(dependencies.size() == 0) return false;
        boolean[] visited = new boolean[n];
        boolean[] inStack = new boolean[n];
        for(int i = 0; i < n; i++) {
            if(visited[i]) continue;
            if(dfs(i, visited, inStack, g)) return true;
        }
        return false;
    }
    
    // true if there is cycle
    boolean bfs(int start, boolean[] inPath, boolean[] visited, List<List<Integer>> g) {
        if(inPath[start]) return true;
        if(visited[start]) return false;
        
        inPath[start] = true;
        visited[start] = true;
        
        for(var n : g.get(start)) {
            if(dfs(n, inPath, visited, g)) return true;
        }
// backtrack, only remove in path because we dont' want to revisit nodes we already visited
        inPath[start] = false;
    }
}

public class Solution {
    public static void main(String[] args) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));

        int n = Integer.parseInt(bufferedReader.readLine().trim());

        int dependenciesRows = Integer.parseInt(bufferedReader.readLine().trim());
        int dependenciesColumns = Integer.parseInt(bufferedReader.readLine().trim());

        List<List<Integer>> dependencies = new ArrayList<>();

        IntStream.range(0, dependenciesRows).forEach(i -> {
            try {
                dependencies.add(
                    Stream.of(bufferedReader.readLine().replaceAll("\\s+$", "").split(" "))
                        .map(Integer::parseInt)
                        .collect(toList())
                );
            } catch (IOException ex) {
                throw new RuntimeException(ex);
            }
        });

        boolean result = Result.hasCircularDependency(n, dependencies);

        System.out.println(result ? 1 : 0);

        bufferedReader.close();
    }
}