java实现拓扑排序的例子

以下是Java实现拓扑排序的例子：

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;

public class TopologicalSort {
    public int[] topoSort(int numCourses, int[][] prerequisites) {
        // 记录每个节点的入度
        int[] inDegree = new int[numCourses];
        // 记录每个节点的后继节点
        ArrayList<Integer>[] nextNodes = new ArrayList[numCourses];
        for (int i = 0; i < numCourses; i++) {
            nextNodes[i] = new ArrayList<>();
        }
        // 构建图
        for (int[] edge : prerequisites) {
            int from = edge[1];
            int to = edge[0];
            inDegree[to]++;
            nextNodes[from].add(to);
        }
        // 将入度为0的节点加入队列
        Queue<Integer> queue = new LinkedList<>();
        for (int i = 0; i < numCourses; i++) {
            if (inDegree[i] == 0) {
                queue.offer(i);
            }
        }
        // 进行拓扑排序
        int[] result = new int[numCourses];
        int index = 0;
        while (!queue.isEmpty()) {
            int curr = queue.poll();
            result[index++] = curr;
            for (int next : nextNodes[curr]) {
                inDegree[next]--;
                if (inDegree[next] == 0) {
                    queue.offer(next);
                }
            }
        }
        // 判断是否存在环
        if (index != numCourses) {
            return new int[0];
        }
        return result;
    }
}

使用方法：

int numCourses = 4;
int[][] prerequisites = {{1, 0}, {2, 0}, {3, 1}, {3, 2}};
TopologicalSort ts = new TopologicalSort();
int[] result = ts.topoSort(numCourses, prerequisites);
for (int i : result) {
    System.out.print(i + " ");
}

输出结果为：0 1 2 3，表示拓扑排序的结果。