merge-two-sorted-lists solution (#2757)

Author: togo26

merge-two-sorted-lists/togo26.js

@@ -0,0 +1,46 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} list1
+ * @param {ListNode} list2
+ * @return {ListNode}
+ */
+
+// TC: O(n + m) / SC: O(1)
+var mergeTwoLists = function (list1, list2) {
+  let mergeHead = null;
+  let mergePointer = null;
+
+  let head1 = list1;
+  let head2 = list2;
+
+  const mergeNode = node => {
+    const temp = node.next;
+    if (!mergeHead) {
+      mergeHead = node;
+      mergePointer = node;
+    } else {
+      mergePointer.next = node;
+      mergePointer = mergePointer.next;
+    }
+    return temp;
+  };
+
+  while (head1 && head2) {
+    if (head1.val <= head2.val) {
+      head1 = mergeNode(head1);
+    } else {
+      head2 = mergeNode(head2);
+    }
+  }
+
+  if (head1) mergeNode(head1);
+  if (head2) mergeNode(head2);
+
+  return mergeHead;
+};