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Author: hajin-kim

0024-swap-nodes-in-pairs/0024-swap-nodes-in-pairs.kt

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+/**
+ * Example:
+ * var li = ListNode(5)
+ * var v = li.`val`
+ * Definition for singly-linked list.
+ * class ListNode(var `val`: Int) {
+ *     var next: ListNode? = null
+ * }
+ */
+class Solution {
+    fun swapPairs(head: ListNode?): ListNode? {
+        val ret = head?.next
+        ret ?: return head
+
+        var prev: ListNode? = null
+        var odd: ListNode? = null
+        var now = head
+        while (now != null) {
+            if (odd == null) {
+                odd = now
+
+                now = now.next
+            } else {
+                prev?.next = now
+                odd.next = now.next
+                now.next = odd
+
+                now = odd.next
+
+                prev = odd
+                odd = null
+            }
+        }
+
+        return ret
+    }
+}