JAVA邻接表实现拓扑排序

package TopSort;

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

/*拓扑序列:对一个有向无环图(Directed Acyclic Graph简称DAG)G进行拓扑排序，是将G中所有顶点排成一个线性
 * 序列，使得图中任意一对顶点u和v，若<u，v> ∈E(G)，则u在线性序列中出现在v之前。
 * 
 */

public class TopSort {
	
	static int[][] map;
	static int[] indegree; // 这n个点的入度
	static int n, m; //顶点数，边数
	static LinkedList<Integer> stack = new LinkedList<Integer>(); //模拟栈

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		m = sc.nextInt();
		map = 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++) {
				map[i][j] = 0;
			}
		}
		int x, y;
		for (int i = 0; i < m; i++) {
			x = sc.nextInt();
			y = sc.nextInt();
			if (map[x][y] == 0) { // 判重边
				map[x][y] = 1;
				indegree[y]++;
			}

		}
		topSort1();  
		topSort2();
	}
	//遍历顺序一：广度遍历
	private static void topSort1() {
		int count = 0; //判断有无回路（是否成环）
		for (int i = 0; i < n; i++) {
			if (indegree[i] == 0) {
				stack.addFirst(i);
				indegree[i] = -1;
			}
		}
		while (!stack.isEmpty()) {
			int p = stack.removeFirst();
			System.out.print(p + " ");
			count++;
			for (int j = 0; j < n; j++) {
				if (map[p][j] == 1) {
					map[p][j] = 0;
					indegree[j]--;
					if (indegree[j] == 0) {
						stack.addFirst(j);
						indegree[j] = -1;
					}
				}
			}
		}
		System.out.println();
		if(count <n) System.out.println("The network has a cycle!"); //当输出的顶点数小于图中的顶点数时，输出有回路信息
		else  System.out.println("The network has not a cycle!");
	}
	//遍历顺序二：深度遍历
	private static void topSort2() {
		int count = 0; //判断有无回路（是否成环）
		for (int i = 0; i < n; i++) {
			if (indegree[i] == 0) {
				stack.addFirst(i);
				indegree[i] = -1;
			}
			while (!stack.isEmpty()) {
				int p = stack.removeFirst();
				System.out.print(p+" ");
				count ++;
				for (int j = 0; j < n; j++) {
					if (map[p][j] == 1) {
						map[p][j] = 0;
						indegree[j]--;
						if (indegree[j] == 0) {
							stack.addFirst(j);
							indegree[j] = -1;
						}
					}
				}
			}
		}
		System.out.println();
		if(count <n) System.out.println("The network has a cycle!"); //当输出的顶点数小于图中的顶点数时，输出有回路信息
		else  System.out.println("The network has not a cycle!");
	}

}
/*
 * 7 8
 * 
 * 0 1
 * 0 3
 * 1 2
 * 1 6
 * 3 6
 * 4 3
 * 4 5
 * 5 6
 * 
 * */