leetcode 206

Author: Kondareddy1209

Leetcode/Leetcode_206.py

@@ -0,0 +1,39 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+
+class Solution:
+    def reverseList(self, head):
+        """
+        Reverse a singly linked list.
+
+        Approach:
+        - Use three pointers: prev, curr (head), and next (implicit)
+        - Iterate through the list and reverse the direction of each node
+
+        Time Complexity: O(n)  -> Traverse the list once
+        Space Complexity: O(1) -> In-place reversal, no extra memory used
+        """
+
+        # 'prev' will become the new head of reversed list
+        prev = None
+
+        # Traverse until head becomes None
+        while head:
+            # Step 1: Store current node
+            curr = head
+
+            # Step 2: Move head to next node
+            # (important to not lose the rest of the list)
+            head = head.next
+
+            # Step 3: Reverse the link
+            curr.next = prev
+
+            # Step 4: Move prev forward
+            prev = curr
+
+        # At the end, prev will be the new head
+        return prev