BSF1

Problem1.java

@@ -0,0 +1,41 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Problem1 {
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        if(root == null) return new ArrayList<>();
+        List<List<Integer>> result = new ArrayList<>();
+        Queue<TreeNode> q = new LinkedList<>();
+        q.add(root);
+
+        while(!q.isEmpty()){
+            int size = q.size();
+            List<Integer> temp = new ArrayList<>();
+            for(int i=0; i<size; i++){
+                TreeNode curr = q.poll();
+                temp.add(curr.val);
+                if(curr.left != null){
+                    q.add(curr.left);
+                }
+                if(curr.right != null){
+                    q.add(curr.right);
+                }
+            }
+            result.add(temp);
+        }
+
+        return result;
+    }
+}

Problem2.java

@@ -0,0 +1,44 @@
+class Problem2 {
+    public boolean canFinish(int numCourses, int[][] prerequisites) {
+
+        int[] indegrees = new int[numCourses];
+        HashMap<Integer, List<Integer>> map = new HashMap<>();
+
+        for(int[] pr : prerequisites){
+            // pr[0] - dependent, pr[1] - independent
+            indegrees[pr[0]]++;
+            map.putIfAbsent(pr[1], new ArrayList<>());
+            map.get(pr[1]).add(pr[0]);
+        }
+
+        int count = 0;
+        Queue<Integer> q = new LinkedList<>();
+
+        for(int i = 0; i < numCourses; i++){
+            if(indegrees[i] == 0){
+                q.add(i);
+                count++;
+            }
+        }
+
+        if(q.isEmpty()) return false;
+        if(count == numCourses) return true;
+
+        while(!q.isEmpty()){
+            int curr = q.poll();
+            List<Integer> dependencies = map.get(curr);
+            if(dependencies != null){
+                for(int dependent : dependencies){
+                    indegrees[dependent]--;
+                    if(indegrees[dependent] == 0){
+                        q.add(dependent);
+                        count++;
+                        if(count == numCourses) return true;
+                    }
+                }
+            }
+        }
+
+        return false;
+    }
+}