done

bfs

@@ -0,0 +1,45 @@
+/**
+ * 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;
+ *     }
+ * }
+ */
+ //TC On . SC On
+class Solution {
+    public List<List<Integer>> levelOrder(TreeNode root) {
+
+        List<List<Integer>> re = new ArrayList<>();
+        Queue<TreeNode> q = new LinkedList<>();
+           if (root == null)
+            return re;
+        q.add(root);
+        while (!q.isEmpty()) {
+
+            List<Integer> li = new ArrayList<>();
+            int size=q.size();
+            for (int i = 0; i < size; i++) {
+
+                TreeNode e = q.poll();
+
+
+                if (null != e.left)
+                    q.add(e.left);
+                if (null != e.right)
+                    q.add(e.right);
+                    li.add(e.val);
+            }
+            re.add(li);
+
+        }
+        return re;
+    }
+}

courseSchedule

@@ -0,0 +1,45 @@
+class Solution {
+    //TC / SC O(V+E)
+    public boolean canFinish(int numCourses, int[][] prerequisites) {
+        int[] indegree = new int[numCourses];
+        HashMap<Integer, List<Integer>> hm = new HashMap<>();
+        //make indegree array and populate map
+        for (int[] pr : prerequisites) {
+            indegree[pr[0]]++;
+            hm.putIfAbsent(pr[1], new ArrayList<>());
+            hm.get(pr[1]).add(pr[0]);
+        }
+
+        //bfs
+        int count = 0;
+        Queue<Integer> q = new LinkedList<>();
+        for (int i = 0; i < numCourses; i++) {
+
+            if (indegree[i] == 0) {
+                q.add(i);
+                count++;
+            }
+        }
+
+         if (count == numCourses)
+                return true;
+
+        while (!q.isEmpty()) {
+
+            int curr = q.poll();
+            List<Integer> children = hm.get(curr);
+            if (null != children) {
+                for (int child : children) {
+                    indegree[child]--;
+                    if (indegree[child] == 0) {
+                        q.add(child);
+                        count++;
+                        if (count == numCourses)
+                            return true;
+                    }
+                }
+            }
+        }
+        return false;
+    }
+}