两个有序链表的合并

#include <stdio.h>
#include <stdlib.h>

typedef struct node 
{
  int id;
  struct node * next;
} node;

node *merge(node *head1, node *head2)
{
  node  *pa = head1;
  node  *pb = head2;
  node  *head;
  node  a; 
  node  *pc = &a;
  
  if (pa == NULL)
    return pb;
  if (pb == NULL) 
    return pa;
  
  head = (pa->id > pb->id) ? pb : pa;
  while (pa && pb)
  {
    if (pa->id > pb->id)
    {
      pc->next = pb;
      pc = pb;
      pb = pb->next;
    }
    else
    {
      pc->next = pa;
      pc = pa;
      pa = pa->next;
    }
  }
  pc->next = pa ? pa : pb;

  return head;
}

 这是一种比较简单的方法，定义一个node类型的a变量，只是为了使得pc指针在第一次时有指向，防止pc称为野指针。