解析

//! 暴力迭代法，不破坏外界列表，没有任何技巧 t:n1+n2,s:n1+n2
class Solution {
 public:
  ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
    ListNode* resList = new ListNode();
    ListNode* node = resList;
    ListNode* node1 = list1;
    ListNode* node2 = list2;
    while (node1 != nullptr || node2 != nullptr) {
      if (node2 == nullptr || node1 != nullptr && node1->val <= node2->val) {
        node->next = new ListNode(node1->val);
        node1 = node1->next;
        node = node->next;
      } else {
        node->next = new ListNode(node2->val);
        node2 = node2->next;
        node = node->next;
      }
    }
    if (resList == nullptr) {
      return nullptr;
    } else {
      node = resList->next;
      delete resList;
      return node;
    }
  }
};