added topological sort problem

Java/graphs/TopologicalSort.java

@@ -0,0 +1,74 @@
+/*There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1.
+You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course bi first if you want to take course ai.
+
+For example, the pair [0, 1], indicates that to take course 0 you have to first take course 1.
+Return true if you can finish all courses. Otherwise, return false.
+
+Example 1:
+Input: numCourses = 2, prerequisites = [[1,0]]
+Output: true
+Explanation: There are a total of 2 courses to take.
+To take course 1 you should have finished course 0. So it is possible.
+Example 2:
+Input: numCourses = 2, prerequisites = [[1,0],[0,1]]
+Output: false
+Explanation: There are a total of 2 courses to take.
+To take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible.
+
+Constraints:
+1 <= numCourses <= 2000
+0 <= prerequisites.length <= 5000
+prerequisites[i].length == 2
+0 <= ai, bi < numCourses
+All the pairs prerequisites[i] are unique. */
+
+import java.util.*;
+
+public class TopologicalSort {
+    public static void main(String[] args) {
+        int numCourses = 2;
+        int[][] prerequisites = {{1, 0}};
+
+        boolean canFinish = canFinish(numCourses, prerequisites);
+        System.out.println("Can finish all courses: " + canFinish);
+    }
+
+
+    public static boolean canFinish(int numCourses, int[][] prerequisites) {
+        int[] indegree = new int[numCourses];
+        List<List<Integer>> adjList = new ArrayList<>();
+        for(int i = 0; i < numCourses; i++){
+            adjList.add(new ArrayList<>());
+        }
+        for(int[] pre : prerequisites){
+            adjList.get(pre[1]).add(pre[0]);
+        }
+        for(int i = 0; i < numCourses; i++){
+            for(int neighbor : adjList.get(i)){
+                indegree[neighbor]++;
+            }
+        }
+        Queue<Integer> q = new LinkedList<>();
+        List<Integer> ans = new ArrayList<>();
+
+        for(int i = 0; i < indegree.length; i++){
+            if(indegree[i] == 0){
+                q.add(i);
+            }
+        }
+
+        while(!q.isEmpty()){
+            int curr = q.poll();
+            ans.add(curr);
+
+            for(int neighbor : adjList.get(curr)){
+                indegree[neighbor]--;
+                if(indegree[neighbor] == 0){
+                    q.add(neighbor);
+                }
+            }
+        }
+
+        return ans.size() == numCourses;
+    }
+}