[Java] 백준 9466번 텀 프로젝트 - DP, case work

https://www.acmicpc.net/problem/9466

9466번: 텀 프로젝트

처음에는 사이클에 구성되지 않는 노드의 개수를 찾는 문제라고 생각했으나

시간복잡도가 n^2가 되어 불가능했기에,

어느 노드에서 출발하더라도 마지막에는 항상 사이클로 연결된다는 점을 이용했다.

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

public class g3_9466 {
    static FastScanner fs = new FastScanner();
    static PrintWriter pw = new PrintWriter(System.out);
    static int T, n, cnt, flag;
    static int[] visit, next;
    static Queue<Integer> route;

    public static void main(String[] args) {
        T = fs.nextInt();
        for (int t=0;t<T;t++){
            n = fs.nextInt();
            visit = new int[n + 1];
            next = new int[n + 1];
            cnt = 0;
            for (int i=1;i<=n;i++) next[i] = fs.nextInt();
            for (int i=1;i<=n;i++){
                route = new LinkedList<>();
                flag = i;
                find(i);
            }
            pw.println(cnt);
        }
        pw.close();
    }

    static void find(int now){
        route.add(now);
        // this node is never visited
        if (visit[now] == 0){
            visit[now] = flag;
            find(next[now]);
        }
        // this node was once visited during this searching
        else if (visit[now] == flag){
            while (!route.isEmpty()){
                if (route.poll() == now) return;
                cnt++;
            }
        }
        // this node was visited during past serching
        else cnt += route.size() - 1;
    }

    // ----------input function----------

    static void sort(int[] a) {
        ArrayList<Integer> L = new ArrayList<>();
        for (int i : a)
            L.add(i);
        Collections.sort(L);
        for (int i = 0; i < a.length; i++)
            a[i] = L.get(i);
    }

    static class FastScanner {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer("");

        String next() {
            while (!st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        int[] readArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        long nextLong() {
            return Long.parseLong(next());
        }
    }
}