reorder-list solution

Author: yyyyyyyyyKim

reorder-list/yyyyyyyyyKim.py

@@ -0,0 +1,42 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def reorderList(self, head: Optional[ListNode]) -> None:
+        """
+        Do not return anything, modify head in-place instead.
+        """
+        # 시간복잡도 o(n), 공간복잡도 O(1)
+        
+        # 리스트 중간 지점 찾기
+        slow, fast = head, head
+
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+            
+        # 중간에서 뒷부분 뒤집기
+        curr = slow.next
+        prev = None
+        slow.next = None
+
+        while curr:
+            next_temp = curr.next
+            curr.next = prev
+            prev = curr
+            curr = next_temp
+            
+        # 앞부분과 뒷부분 합치기
+        first, second = head, prev
+
+        while second:
+            temp1 = first.next
+            temp2 = second.next
+            
+            first.next = second
+            second.next = temp1
+            
+            first = temp1
+            second = temp2