BFS-1

problem1.py

@@ -0,0 +1,30 @@
+# Space Complexity: O(N)
+# Time Complexity: O(N)
+
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+        if not root: return []
+        q = collections.deque()
+        q.append(root)
+        ans = []
+        while q: 
+            s = len(q)
+            li = []
+            for _ in range(s):
+                node = q.popleft()
+                li.append(node.val)
+                if node.left: 
+                    q.append(node.left)
+                if node.right: 
+                    q.append(node.right)
+            ans.append(li)
+
+
+        return ans
+

problem2.py

@@ -0,0 +1,30 @@
+# Time Complexity: O(N)
+# Space Complexity: O(N)
+class Solution:
+    def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool:
+
+        adj = collections.defaultdict(list)
+        ind = [0] * numCourses
+
+        for u,v in prerequisites: 
+            adj[u].append(v)
+            ind[v]+=1
+
+        q = collections.deque()
+
+        for i in range(numCourses): 
+            if ind[i] == 0: 
+                q.append(i)
+
+
+        while q: 
+            node = q.popleft()
+            for neigh in adj[node]: 
+                ind[neigh]-=1
+                if ind[neigh] == 0: 
+                    q.append(neigh)
+
+        return sum(ind) == 0
+
+
+