feat : reverse-linked-list

Author: ekgns33

reverse-linked-list/ekgns33.java

@@ -0,0 +1,37 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ *
+ *
+ * input : head of linked list
+ * output : reversed linked list
+ *
+ * solution1)
+ * set fast pointer and slow pointer
+ * iterate through the linked list
+ *  set fast pointer's next to slow pointer
+ *
+ * tc : O(n)
+ * sc : O(1)
+ */
+class Solution {
+  public ListNode reverseList(ListNode head) {
+    if(head == null) return head;
+    ListNode curr = head;
+    ListNode prev = null;
+    while(curr.next != null) {
+      ListNode next = curr.next;
+      curr.next = prev;
+      prev = curr;
+      curr = next;
+    }
+    curr.next = prev;
+    return curr;
+  }
+}