Level order, course schedule

leetcode-102.py

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+#102. Binary Tree Level Order Traversal
+# https://leetcode.com/problems/binary-tree-level-order-traversal/
+
+# T.C: O(n)
+# S.C: 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
+from collections import deque
+class Solution:
+    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+
+        if not root:
+            return []
+
+        q = deque([])
+        q.append(root)
+        res = []
+        while q:
+            size = len(q)
+            curr = []
+            for i in range(size):
+                item = q.popleft()
+                curr.append(item.val)
+                if item.left:
+                    q.append(item.left)
+                if item.right:
+                    q.append(item.right)
+
+            res.append(curr)
+
+        return res

leetcode-207.py

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+# 207. Course Schedule
+# https://leetcode.com/problems/course-schedule/
+# 
+# T.C: O(n)
+# S.C: O(n)
+
+
+from collections import defaultdict, deque
+class Solution:
+    def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool:
+
+        indegree = [0 for i in range(numCourses)]
+        adj = defaultdict(list)
+
+        for el in prerequisites:
+            adj[el[1]]. append(el[0])
+            indegree[el[0]] += 1
+        q = deque()
+        for i in range(numCourses):
+            if indegree[i] == 0:
+                q.append(i)
+
+        if len(q) == numCourses:
+            return True
+
+        while q:
+            curr = q.popleft()
+
+            for child in adj[curr]:
+                indegree[child] -= 1
+                if indegree[child] == 0:
+                    q.append(child)
+        print(indegree, q)
+        for i in range(numCourses):
+            if indegree[i] != 0:
+                return False
+
+        return True