merge two sorted lists solution

Author: hyer0705

merge-two-sorted-lists/hyer0705.ts

@@ -0,0 +1,44 @@
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function mergeTwoLists(list1: ListNode | null, list2: ListNode | null): ListNode | null {
+  if (!list1 && !list2) return null;
+
+  if (!list1) return list2;
+  if (!list2) return list1;
+
+  const dummyHead = new ListNode(-101);
+  let tail = dummyHead;
+
+  let pointerOne: ListNode | null = list1;
+  let pointerTwo: ListNode | null = list2;
+
+  while (pointerOne && pointerTwo) {
+    if (pointerOne.val <= pointerTwo.val) {
+      tail.next = pointerOne;
+      pointerOne = pointerOne.next;
+    } else {
+      tail.next = pointerTwo;
+      pointerTwo = pointerTwo.next;
+    }
+
+    tail = tail.next;
+  }
+
+  if (pointerOne) {
+    tail.next = pointerOne;
+  } else {
+    tail.next = pointerTwo;
+  }
+
+  return dummyHead.next;
+}