Create 1721-swapping-nodes-in-a-linked-list.js

Author: everthis

1721-swapping-nodes-in-a-linked-list.js

@@ -0,0 +1,40 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @param {number} k
+ * @return {ListNode}
+ */
+const swapNodes = function(head, k) {
+  const dummy = new ListNode()
+  dummy.next = head
+  const arr = []
+  let cur = head
+  while(cur) {
+    arr.push(cur)
+    cur = cur.next
+  }
+  const n = arr.length
+  if(k < 1 || k > n) return dummy.next
+  let first = arr[k - 1], second = arr[n - k]
+  
+  arr[k - 1] = second
+  arr[n - k] = first
+    
+  dummy.next = arr[0]
+  let pre = arr[0]
+  for(let i = 1, len = arr.length; i < len; i++) {
+     const tmp = arr[i]
+     pre.next = tmp
+     pre = tmp
+  }
+  
+  pre.next = null
+ 
+  return dummy.next
+};