completed

binarytreelevelordertraversal.py

@@ -0,0 +1,30 @@
+# 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
+
+
+# Time Complexity: O(n)
+# Space Complexity: O(h)
+class Solution:
+    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+        if not root:
+            return []
+
+        self.result = []
+
+        def helper(root, level):
+            if not root:
+                return
+
+            if len(self.result) == level:
+                self.result.append([])
+
+            self.result[level].append(root.val)
+            helper(root.left, level + 1)
+            helper(root.right, level + 1)
+
+        helper(root, 0)
+        return self.result

courseschedule.py

@@ -0,0 +1,40 @@
+# Time Complexity: O(V+E)
+# Space Complexity: O(V+E)
+class Solution:
+    def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool:
+        indegrees = [0] * numCourses
+        graph = defaultdict(list)
+
+        for pre in prerequisites:
+            indegrees[pre[0]] += 1
+            graph[pre[1]].append(pre[0])
+
+        queue = deque()
+        count = 0
+
+        for i in range(len(indegrees)):
+            if indegrees[i] == 0:
+                queue.append(i)
+                count += 1
+
+        if count == numCourses:
+            return True
+
+        if not queue:
+            return False
+
+        while queue:
+            curr = queue.popleft()
+            dependencies = graph[curr]
+            if dependencies:
+                for dep in dependencies:
+                    indegrees[dep] -= 1
+                    if indegrees[dep] == 0:
+                        queue.append(dep)
+                        count += 1
+
+                    if count == numCourses:
+                        return True
+
+        return False
+