[printjin-gmailcom] week 12 solutions

non-overlapping-intervals/printjin-gmailcom.py

@@ -0,0 +1,13 @@
+from typing import List
+
+class Solution:
+    def eraseOverlapIntervals(self, intervals: List[List[int]]) -> int:
+        intervals.sort(key=lambda x: x[1])
+        count = 0
+        end = float('-inf')
+        for start, finish in intervals:
+            if start < end:
+                count += 1
+            else:
+                end = finish
+        return count

number-of-connected-components-in-an-undirected-graph/printjin-gmailcom.py

@@ -0,0 +1,18 @@
+from typing import (
+    List,
+)
+
+class Solution:
+    def count_components(self, n: int, edges: List[List[int]]) -> int:
+        parent = [i for i in range(n)]
+        def find(x):
+            if parent[x] != x:
+                parent[x] = find(parent[x])
+            return parent[x]
+        for a, b in edges:
+            root_a = find(a)
+            root_b = find(b)
+            if root_a != root_b:
+                parent[root_a] = root_b
+                n -= 1
+        return n

remove-nth-node-from-end-of-list/printjin-gmailcom.py

@@ -0,0 +1,11 @@
+class Solution:
+    def removeNthFromEnd(self, head, n):
+        dummy = ListNode(0, head)
+        fast = slow = dummy
+        for _ in range(n):
+            fast = fast.next
+        while fast.next:
+            fast = fast.next
+            slow = slow.next
+        slow.next = slow.next.next
+        return dummy.next

same-tree/printjin-gmailcom.py

@@ -0,0 +1,9 @@
+class Solution:
+    def isSameTree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
+        if not p and not q:
+            return True
+        if not p or not q:
+            return False
+        if p.val != q.val:
+            return False
+        return self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)

serialize-and-deserialize-binary-tree/printjin-gmailcom.py

@@ -0,0 +1,26 @@
+class Codec:
+    def serialize(self, root):
+        def dfs(node):
+            if not node:
+                vals.append("None")
+                return
+            vals.append(str(node.val))
+            dfs(node.left)
+            dfs(node.right)
+
+        vals = []
+        dfs(root)
+        return ",".join(vals)
+
+    def deserialize(self, data):
+        def dfs():
+            val = next(vals)
+            if val == "None":
+                return None
+            node = TreeNode(int(val))
+            node.left = dfs()
+            node.right = dfs()
+            return node
+
+        vals = iter(data.split(","))
+        return dfs()