拓扑排序 JAVA

判断是否成环 JAVA 代码实现

import java.util.LinkedList;
import java.util.Scanner;

public class Hello{
	static int[][]mp;
	static int[] indegree;
	static int N, M;
	static LinkedList<Integer> list = new LinkedList<Integer>();
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		N = sc.nextInt();
		M = sc.nextInt();
		mp = new int[N][N];
		indegree = new int[N];
		for(int i = 0; i < N; i ++) {
			indegree[i] = 0;
			for(int j = 0; j < N; j ++) {
				mp[i][j] = 0;
			}
		}
		
		int x, y;
		for(int i = 0; i < M; i ++) {
			x = sc.nextInt();
			y = sc.nextInt();
			if(mp[x][y] == 0) {
				mp[x][y] = 1;
				indegree[y] ++;
			}
		}
		
		topSort();
		
	}
	
	private static void topSort() {
		int cnt = 0;
		for(int i = 0; i < N; i ++) {
			if(indegree[i] == 0) {
				list.addFirst(i);
				indegree[i] = -1;
			}
		}
		
		while(!list.isEmpty()) {
			int p = list.removeFirst();
			System.out.print(p + " ");
			cnt ++;
			for(int j = 0; j < N; j ++) {
				if(mp[p][j] == 1) {
					mp[p][j] = 0;
					indegree[j] --;
					if(indegree[j] == 0) {
						list.addFirst(j);
						indegree[j] = -1;
					}
				}
			}
		}
		
		System.out.println();
		if(cnt < N) System.out.println("Cycleeeeee!");
		else System.out.println("Nooooooooo!");
		
	}
	
}
 

　　但是上述是建立邻接矩阵的写法 当 N 太大的时候就不是很好了 所以可以用链表来存边和边的关系 会节省内存 所以以下是链表存图并判断拓扑关系

import java.util.concurrent.ArrayBlockingQueue;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class Hello{
	
	static int N, M;
	static int[] v;
	static int[] nx;
	static int[] h;
	static int[] ans;
	static int[] in;
	static int cnt, sz;
	static LinkedList<Integer> list = new LinkedList<Integer>();
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		v = new int[100010];
		nx = new int[100010];
		h = new int[100010];
		in = new int[100010];
		N = sc.nextInt();
		M = sc.nextInt();
		
		init();
		
		for(int i = 0; i < M; i ++) {
			int x, y;
			x = sc.nextInt();
			y = sc.nextInt();
			add(x, y);
		}
		
		topSort();
		
	}
	
	public static void init() {
		for(int i = 0; i < 100010; i ++) {
			h[i] = -1;
			in[i] = 0;
		}
		
		sz = 0;
		
	}
	
	public static void add(int a, int b) {
		v[sz] = b;
	    nx[sz] = h[a];
	    h[a] = sz;
	    in[b] ++;
	    sz ++;
	}
	
	public static void topSort() {
		for(int i = 0; i < N; i ++) {
			if(in[i] == 0) list.addFirst(i);
		}
		
		while(!list.isEmpty()) {
			int tp = list.removeFirst();
			System.out.print(tp + " ");
			cnt ++;
			
			for(int i = h[tp]; i != -1; i = nx[i]) {
				in[v[i]] --;
				if(in[v[i]] == 0) list.addFirst(v[i]);
			}
			
		}
		
		System.out.println();
		if(cnt != N) 
			System.out.println("Circleeeeeeeeee");
		else System.out.println("Noooooooooo");
	}
	
}