C++/21. Merge Two Sorted Lists 编译出错

[Ming-Qin-tech]

/**

• Definition for singly-linked list.
• struct ListNode {

• int val;
  

• ListNode *next;
  

• ListNode(int x) : val(x), next(NULL) {}
  

• };
  /
  class Solution {
  public:
  ListNode mergeTwoLists(ListNode* l1, ListNode* l2) {
  if(l1 != NULL && l2 != NULL) {
  ListNode *p = l1;
  ListNode *q = l2;
  ListNode *t, *h; //t为新链表的连接指针，h为新链表的头指针
  if(p->val > q->val) {
  t = q;
  h = q;
  q = q->next;
  } else {
  t = p;
  h = p;
  p = p->next;
  }
  while(p != NULL && q != NULL) {
  if(p->val > q->val) {
  t->next = q;
  t = t->next;
  q = q->next;
  } else {
  t->next = p;
  t = t->next;
  p = p->next;
  }
  }
  while(p != NULL && q == NULL) {
  t->next = p;
  t = t->next;
  p = p->next;
  }
  while(p == NULL && q != NULL) {
  t->next = q;
  t = t->next;
  q = q->next;
  }
  while(p == NULL && q == NULL) {
  return h;
  }
  }
  if(l1 == NULL && l2 != NULL) {
  return l2;
  }
  if(l1 != NULL && l2 == NULL) {
  return l1;
  }
  if(l1 == NULL && l2 == NULL) {
  return NULL;
  }
  return NULL;
  }
  };
  所不同的就是line 59加一行： return NULL；
  虽然用不到，但是如果不加就会编译出错：
  error:control reaches end of non-void function[-Werror=return-type]