Tarjan 模板 缩点 受欢迎的牛 Java实现

我讨厌🐂......

受欢迎的牛

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.LinkedList;
import java.util.StringTokenizer;

public class Main implements Runnable{
static int[] dfn,low,parent;
static int[] stack,colorTypeCnt,pointColor,outDegrees;
static int colorTypeName,visitCnt,stackIdx;
static boolean[] mark,isInStack;
static LinkedList[] adj;

static class Edge{
    int from,to;

    public Edge(int from, int to) {
        this.from = from;
        this.to = to;
    }
}

public static void main(String[] args) {
    new Thread(null,new Main(),"",1<<29).start();
}

@Override
public void run() {
    try {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());

        int n = Integer.parseInt(st.nextToken());
        int m = Integer.parseInt(st.nextToken());

        dfn = new int[n+1];
        low = new int[n+1];
        parent = new int[n+1];
        stack = new int[n+1];
        colorTypeCnt = new int[n+1];
        pointColor = new int[n+1];
        outDegrees = new int[n+1];
        mark = new boolean[n+1];
        isInStack = new boolean[n+1];

        adj = new LinkedList[n+1];
        for(int i = 0;i<adj.length;i++){
            adj[i] = new LinkedList<>();
        }

        int from,to;
        for(int i = 0;i<m;i++){
            st = new StringTokenizer(br.readLine());
            from = Integer.parseInt(st.nextToken());
            to = Integer.parseInt(st.nextToken());
            adj[from].add(new Edge(from,to));
        }

        for(int i = 1;i<=n;i++){
            if(!mark[i]){
                dfs(i);
            }
        }

        for(int i = 1;i<=n;i++){
            for(Edge e:adj[i]){
                if(pointColor[i]!=pointColor[e.to]){
                    outDegrees[pointColor[i]]++;
                }
            }
        }

        int resultColorName=0;
        for(int i = 1;i<=colorTypeName;i++){
            if(outDegrees[i] == 0){
                if(resultColorName!=0){
                    System.out.println(0);
                    return;
                }
                resultColorName = i;
            }
        }
        System.out.println(colorTypeCnt[resultColorName]);

    }catch (Exception e){
        e.printStackTrace();
    }
}

private static void dfs(int start){
    dfn[start] = low[start] = visitCnt;
    parent[start] = -1;
    stack[++stackIdx] = start;
    isInStack[start] = true;
    mark[start] = true;
    for(Edge e:adj[start]){
        int to = e.to;
        if(!mark[to]){
            mark[to] = true;
            parent[to] = start;
            dfs0(to);
        }
    }

    if(dfn[start] == low[start]){
        colorTypeName++;
        do{
            pointColor[stack[stackIdx]] = colorTypeName;
            colorTypeCnt[colorTypeName]++;
            isInStack[stack[stackIdx]] = false;
            stackIdx--;
        }while (start!=stack[stackIdx+1]);
    }
}

private static void dfs0(int from){
    dfn[from] = low[from] = ++visitCnt;
    stack[++stackIdx] = from;
    isInStack[from] = true;
    for(Edge e:adj[from]){
        int to = e.to;
        if(!mark[to]){
            mark[to] = true;
            parent[to] = from;
            dfs0(to);
            low[from] = Math.min(low[from],low[to]);
        }
        else{
            low[from] = Math.min(low[from],dfn[to]);
        }
    }

    if(dfn[from]==low[from]){
        colorTypeName++;
        do{
            pointColor[stack[stackIdx]] = colorTypeName;
            colorTypeCnt[colorTypeName] ++;
            isInStack[stack[stackIdx]] = false;
            stackIdx--;
        }while (from !=stack[stackIdx+1]);
    }
}

}