1. Merge Two Sorted Lists

Author: Sunjae95

merge-two-sorted-lists/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * queue
+ *
+ * n: length of list1 + list2
+ * time complexity: O(n)
+ * space complexity: O(n)
+ */
+var mergeTwoLists = function (list1, list2) {
+  ListNode.prototype.tail = null;
+
+  ListNode.prototype.isLast = function () {
+    return this.val === 0 && this.next === null;
+  };
+
+  ListNode.prototype.pop = function () {
+    const value = this.val;
+    this.val = this.next ? this.next.val : 0;
+    this.next = this.next ? this.next.next : null;
+    return value;
+  };
+
+  ListNode.prototype.push = function (value) {
+    const node = new ListNode(value);
+    if (this.isLast()) {
+      this.val = value;
+      return;
+    }
+
+    if (this.tail === null) {
+      this.next = node;
+      this.tail = node;
+    } else {
+      this.tail.next = node;
+      this.tail = node;
+    }
+  };
+
+  if (list1 === null && list2 === null) return null;
+  if (list1 === null || list2 === null) return list1 ? list1 : list2;
+
+  const answer = new ListNode();
+
+  while (!(list1.isLast() && list2.isLast())) {
+    if (list1.isLast()) {
+      const value = list2.pop();
+      answer.push(value);
+      continue;
+    }
+    if (list2.isLast()) {
+      const value = list1.pop();
+      answer.push(value);
+      continue;
+    }
+    if (list1.val <= list2.val) {
+      const value = list1.pop();
+      answer.push(value);
+      continue;
+    }
+    if (list2.val < list1.val) {
+      const value = list2.pop();
+      answer.push(value);
+      continue;
+    }
+  }
+
+  return answer;
+};