From a74d1468da923687be32c1cdb35ae210587b465f Mon Sep 17 00:00:00 2001
From: YOUNGJIN NA <120540450+ppxyn1@users.noreply.github.com>
Date: Fri, 30 Jan 2026 17:21:20 +0900
Subject: [PATCH] [:solved] three problems

---
 non-overlapping-intervals/ppxyn1.py        | 16 ++++++++++++++
 remove-nth-node-from-end-of-list/ppxyn1.py | 25 ++++++++++++++++++++++
 same-tree/ppxyn1.py                        | 21 ++++++++++++++++++
 3 files changed, 62 insertions(+)
 create mode 100644 non-overlapping-intervals/ppxyn1.py
 create mode 100644 remove-nth-node-from-end-of-list/ppxyn1.py
 create mode 100644 same-tree/ppxyn1.py

diff --git a/non-overlapping-intervals/ppxyn1.py b/non-overlapping-intervals/ppxyn1.py
new file mode 100644
index 0000000000..6914c6a4e4
--- /dev/null
+++ b/non-overlapping-intervals/ppxyn1.py
@@ -0,0 +1,16 @@
+# idea: - 
+# Time Complexity: O(n log n)
+class Solution:
+    def eraseOverlapIntervals(self, intervals: List[List[int]]) -> int:
+        intervals.sort()
+        cnt = 0
+        prevEnd = intervals[0][1]
+        for start, end in intervals[1:]:
+            if start >= prevEnd:
+                prevEnd = end
+            else:
+                cnt += 1
+                prevEnd = min(end, prevEnd)
+        return cnt
+
+
diff --git a/remove-nth-node-from-end-of-list/ppxyn1.py b/remove-nth-node-from-end-of-list/ppxyn1.py
new file mode 100644
index 0000000000..e9e3fb2d14
--- /dev/null
+++ b/remove-nth-node-from-end-of-list/ppxyn1.py
@@ -0,0 +1,25 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+
+# idea : Two pointer
+# Time Complexity : O(length(list))
+class Solution:
+    def removeNthFromEnd(self, head, n):
+        dummy = ListNode()
+        dummy.next = head
+        fast = slow = dummy
+
+        for _ in range(n+1):
+            fast = fast.next
+
+        while fast:
+            fast = fast.next
+            slow = slow.next
+
+        slow.next = slow.next.next
+        return dummy.next
+
+
diff --git a/same-tree/ppxyn1.py b/same-tree/ppxyn1.py
new file mode 100644
index 0000000000..c795002efd
--- /dev/null
+++ b/same-tree/ppxyn1.py
@@ -0,0 +1,21 @@
+# 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
+
+# idea : DFS
+# Inorder method loses structural information, which is not suitable for it.
+# Time Complexity: O(p+q) 
+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))
+