c - 在 C 代码中从队列中读取给定元素

Question

我找到了这个简单的队列代码，我正在尝试更改一些东西。由于是西类牙语，所以我翻译了希望你能看懂。

#include <stdio.h>
#include <Windows.h>

/* Returns "a - b" in seconds */
double performancecounter_diff(LARGE_INTEGER *a, LARGE_INTEGER *b)
{
LARGE_INTEGER freq;
QueryPerformanceFrequency(&freq);
return (double)(a->QuadPart - b->QuadPart) / (double)freq.QuadPart;
}


typedef struct _nodo {
int value;
struct _nodo *next;
} TypeNodo;

typedef TypeNodo *pNodo;

/* Queues functions */
void Insert(pNodo *first, pNodo *last, int v);
int Seek(pNodo *first, pNodo *last, int v);

int main() {
LARGE_INTEGER t_ini, t_fin;
double secs;
QueryPerformanceCounter(&t_ini);
pNodo first = NULL, last = NULL;
int x = 1;
while (x <= 80)
{
    Insert(&first, &last, x);
    x++;
}
printf("%d", Seek(&first, &last,18));
printf("%d", Seek(&first, &last, 2));

QueryPerformanceCounter(&t_fin);
secs = performancecounter_diff(&t_fin, &t_ini);
printf("Algoritmo de manejo de brazo por FCFS: \n");
printf("%.16g milisegundos\n", secs * 1000.0);
system("pause");
return 0;
}

void Insert(pNodo *first, pNodo *last, int v) {
pNodo New;

/* Create a new nodo and allocate it */
New = (pNodo)malloc(sizeof(TypeNodo));
New->value = v;
/* This will be the last nodo and will point to NULL */
New->next = NULL;
/* If queue isn't empty, then add the new nodo next to the last one */
if (*last) (*last)->next = New;
/* Now, the last element of the queue is the new one */
*last = New;
/* If first is NULL, the queue is empty and the first will point to the new nodo,     too */
if (!*first) *first = New;
    }

    int Seek(pNodo *first, pNodo *last, int v) {
pNodo nodo, nodo_aux; /* Extra variable to manipulate the nodo */
int a;      /* Extra variable for return */

/* Nodo points to the first element of the queue */
nodo = *first;
nodo_aux = nodo;
if (!nodo) return 0; /* If no nodos in the queue, retunrs 0 */
while (*first != NULL)
{
    if (nodo->value == v)
    {
        /* Storing return value */
        a = nodo->value;
        return a;
    }
    /* Assign to the first nodo the second one address */
    a = *first = nodo->next;        
}   
/* Free the nodo */
free(nodo);
/* If queue is empty, last must be */
if (!*first) *last = NULL;
return NULL;
}

请注意，下面的函数是原始函数，上面的函数是我试图修改的函数，以便在调用该函数时通过提供它来在队列中查找元素。

//int Seek(pNodo *first, pNodo *last) {
//  pNodo nodo; /* variable auxiliar para manipular nodo */
//  int a;      /* variable auxiliar para retorno */
//
//  /* Nodo apunta al primer elemento de la fila */
//  nodo = *first;
//  if (!nodo) return 0; /* Si no hay nodos en la fila retornamos 0 */
//  /* Asignamos al primer nodo la dirección del segundo nodo */
//  *first = nodo->next;
//  /* Guardamos el value de retorno */
//  a = nodo->value;
//  /* Borrar el nodo */
//  free(nodo);
//  /* Si la cola quedó vacía, last debe ser NULL también */
//  if (!*first) *last = NULL;
//  return a;
//}

当我运行所有代码时，控制台什么也没显示。我不知道我在 Seek() 中遗漏了什么。任何帮助将不胜感激。

Answer 1

它比你简单得多。

int Seek(pNodo first, int v)
{
   while (first != NULL)
   {
      if (first->value == v)
      {
         return v;
      }
      first = first->next;        
   }   

   /* Didn't find the value */
   return 0;
}

更好的选择是返回包含值的节点。如果值不在队列中，则返回 NULL。 (感谢 M Oehm 的建议)

pNode Seek(pNodo first, int v)
{
   while (first != NULL)
   {
      if (first->value == v)
      {
         return first;
      }
      first = first->next;        
   }   

   /* Didn't find the value */
   return NULL;
}