upd

Author: ironchef001

python/0199-binary-tree-right-side-view.me.py

@@ -0,0 +1,29 @@
+# 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 rightSideView(self, root: Optional[TreeNode]) -> List[int]:
+        if not root:
+            return []
+
+        res = defaultdict(list)
+        q = deque()
+        q.append([root, 0])
+
+        while q:
+            node, level = q.popleft()
+            if node:
+                res[level].append(node.val)
+                q.append([node.left, level+1])
+                q.append([node.right, level+1])
+                   
+        keys = list(res.keys())
+        keys.sort()
+        answer = []
+        for key in keys:
+            answer.append(res[key][-1])
+
+        return answer

python/0210-course-schedule-ii.py

@@ -26,3 +26,14 @@ def dfs(crs):
             if dfs(c) == False:
                 return []
         return output
+
+# visit to track course that all prereq have been solved
+# cycle is to introduced to detect the cycle
+#   dfs
+#       if already in cycle, return False
+#       then temporarily add it to cycle
+#       walk over each prereq, 
+#           if all pass, remove from cycle
+#           if one prereq fails, 
+#               it will never be removed from cycle
+#               nex time, dfs will fail immediately

python/0235-lowest-common-ancestor-of-a-binary-search-tree.me.py

@@ -0,0 +1,19 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
+        def dfs(node):
+            if node.val > p.val and node.val > q.val:
+                node = node.left
+            elif node.val < p.val and node.val < q.val:
+                node = node.right
+            else:
+                return node
+            return dfs(node)
+        
+        return dfs(root)