TopoSort-Snippet3.java

import java.util.ArrayList;
import java.util.List;
class Solution {
    public boolean canFinish(int numTasks, int[][] prerequisites) {
        List<Integer>[] adjacencyList = new ArrayList[numTasks];
        int[] prereqCount = new int[numTasks];
        for (int i = 0; i < prerequisites.length; i++) {
            if(adjacencyList[prerequisites[i][1]] == null) {
                adjacencyList[prerequisites[i][1]] = new ArrayList<>();
            }
            adjacencyList[prerequisites[i][1]].add(prerequisites[i][0]);
            prereqCount[prerequisites[i][0]]++;
        }
        boolean proceed = true;
        while (proceed) {
            proceed = false;
            for (int i = 0; i < numTasks; i++) {
                if (prereqCount[i] == 0 && adjacencyList[i] != null) {
                    for (int task : adjacencyList[i]) {
                        prereqCount[task]--;
                    }
                    adjacencyList[i] = null;
                }
            }
            for (int i = 0; i < numTasks; i++) {
                if (prereqCount[i] == 0 && adjacencyList[i] != null) {
                    proceed = true;
                    break;
                }
            }
        }
        for (int i = 0; i < numTasks; i++) {
            if (adjacencyList[i] != null) {
                return false;
            }
        }
        return true;

    }

}