Completed s30 BFS-1

Binarytreelevelordertraversal.py

@@ -0,0 +1,29 @@
+from collections import deque
+
+class Solution:
+    def levelOrder(self, root):
+        if not root:
+            return []
+
+        res = []
+        q = deque([root])
+
+        while q:
+            level = []
+            size = len(q)
+
+            for _ in range(size):
+                node = q.popleft()
+                level.append(node.val)
+
+                if node.left:
+                    q.append(node.left)
+                if node.right:
+                    q.append(node.right)
+
+            res.append(level)
+
+        return res
+
+    # TC - O(n)
+    # SC - O(n)

courseschedule.py

@@ -0,0 +1,42 @@
+from collections import deque
+
+class Solution:
+    def canFinish(self, numCourses, prerequisites):
+        graph = {i: [] for i in range(numCourses)}
+        indegree = [0] * numCourses
+
+        for course, prereq in prerequisites:
+            graph[prereq].append(course)
+            indegree[course] += 1
+
+        q = deque()
+
+        for i in range(numCourses):
+            if indegree[i] == 0:
+                q.append(i)
+
+        visited = 0
+
+        while q:
+            node = q.popleft()
+            visited += 1
+
+            for nei in graph[node]:
+                indegree[nei] -= 1
+
+                if indegree[nei] == 0:
+                    q.append(nei)
+
+        return visited == numCourses
+
+    # TC - O(V+E)
+    # Build graph O(V)
+    # Build edges O(E)
+    # Initialize queue O(V)
+    # BFS O(V + E)
+    # Total TC O(V + E)
+
+    # SC - O(V+E)
+    # Adjacency list: O(V + E)
+    # Indegree array: O(V)
+    # Queue: up to O(V)