[sejineer] Week 08 solutions

clone-graph/sejineer.py

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+"""
+시간 복잡도: O(V + E) V: 노드 개수, E: 간선 개수
+공간 복잡도: O(V)
+"""
+from collections import deque
+from typing import Optional
+class Solution:
+    def cloneGraph(self, node: Optional['Node']) -> Optional['Node']:
+        if not node:
+            return
+
+        clone = Node(node.val)
+        vis = {node: clone}
+        queue = deque([node])
+
+        while queue:
+            cur = queue.popleft()
+            for nxt in cur.neighbors:
+                if nxt not in vis:
+                    vis[nxt] = Node(nxt.val)
+                    queue.append(nxt)
+                vis[cur].neighbors.append(vis[nxt])
+        return clone

palindromic-substrings/sejineer.py

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+"""
+시간 복잡도: O(N^2)
+공간 복잡도: O(1)
+"""
+class Solution:
+    def countSubstrings(self, s: str) -> int:
+        result = 0
+        def count_palindrome(left: int, right: int):
+            count = 0
+            while left >= 0 and right < len(s) and s[left] == s[right]:
+                count += 1
+                left -= 1
+                right += 1
+            return count
+
+        for i in range(len(s)):
+            result += count_palindrome(i, i)
+            result += count_palindrome(i, i + 1)
+        return result

reverse-bits/sejineer.py

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+"""
+시간 복잡도: O(1)
+공간 복잡도: O(1)
+"""
+class Solution:
+    def reverseBits(self, n: int) -> int:
+        result = 0
+        for _ in range(32):
+            result <<= 1
+            result |= n & 1
+            n >>= 1
+        return result