由於通過順序表代碼的複用實現隊列的過程中,進隊列要從隊列的最後一個元素進入,所以造成時間複雜度加大,現通過引進front、rear優化隊列實現方法
front:代表頭元素的下標
rear:代表隊尾下一個元素的下標
一、SeqQueue.h
#ifndef _SEQQUEUE_H_
#define _SEQQUEUE_H_
typedef void SeqQueue;
SeqQueue* SeqQueue_Create(int capacity); //創建隊列
void SeqQueue_Destroy(SeqQueue* queue); //銷燬隊列
void SeqQueue_Clear(SeqQueue* queue); //清空隊列
int SeqQueue_Append(SeqQueue* queue, void* item); //進隊列
void* SeqQueue_Retrieve(SeqQueue* queue); //出隊列
void* SeqQueue_Header(SeqQueue* queue); //獲取隊列的頭元素
int SeqQueue_Length(SeqQueue* queue); //獲取隊列當前的長度
int SeqQueue_Capacity(SeqQueue* queue); //獲取當前的容量
#endif
二、SeqQueue.c
#include <stdio.h>
#include <malloc.h>
#include "SeqQueue.h"
typedef unsigned int TSeqQueueNode;
typedef struct _tag_SeqQueue //定義一個結構體
{
int capacity;
int length;
int front; //始終代表隊頭的下標
int rear; //隊尾下一個元素的下標
TSeqQueueNode* node;
} TSeqQueue;
SeqQueue* SeqQueue_Create(int capacity) // O(1)
{
TSeqQueue* ret = NULL;
if( capacity >= 0 )
{
ret = (TSeqQueue*)malloc(sizeof(TSeqQueue) + sizeof(TSeqQueueNode) * capacity);
}
if( ret != NULL )
{
ret->capacity = capacity;
ret->length = 0;
ret->front = 0;
ret->rear = 0;
ret->node = (TSeqQueueNode*)(ret + 1);
}
return ret;
}
void SeqQueue_Destroy(SeqQueue* queue) // O(1)
{
free(queue);
}
void SeqQueue_Clear(SeqQueue* queue) // 清空隊列
{
TSeqQueue* sQueue = (TSeqQueue*)queue;
if( sQueue != NULL ) //當隊列爲空時,front與rear都爲0
{
sQueue->length = 0;
sQueue->front = 0;
sQueue->rear = 0;
}
}
int SeqQueue_Append(SeqQueue* queue, void* item) // O(1)
{
TSeqQueue* sQueue = (TSeqQueue*)queue;
int ret = (sQueue != NULL) && (item != NULL);
ret = ret && (sQueue->length + 1 <= sQueue->capacity); //判斷隊列是否滿了
if( ret )
{
sQueue->node[sQueue->rear] = (TSeqQueueNode)item;//將入隊列的元素賦值給rear下標的元素node
sQueue->rear = (sQueue->rear + 1) % sQueue->capacity; //將rear下標加一
sQueue->length++; //長度加一
}
return ret;
}
void* SeqQueue_Retrieve(SeqQueue* queue) // O(1)
{
TSeqQueue* sQueue = (TSeqQueue*)queue;
void* ret = SeqQueue_Header(queue);
if( ret != NULL ) //判斷隊列的頭一個元素是否存在
{
sQueue->front = (sQueue->front + 1) % sQueue->capacity;//將front加一的元素賦值給front元素
sQueue->length--; //長度減一
}
return ret;
}
void* SeqQueue_Header(SeqQueue* queue) // O(1)
{
TSeqQueue* sQueue = (TSeqQueue*)queue;
void* ret = NULL;
if( (sQueue != NULL) && (sQueue->length > 0) )
{
ret = (void*)(sQueue->node[sQueue->front]);
}
return ret;
}
int SeqQueue_Length(SeqQueue* queue) // O(1)
{
TSeqQueue* sQueue = (TSeqQueue*)queue;
int ret = -1;
if( sQueue != NULL )
{
ret = sQueue->length;
}
return ret;
}
int SeqQueue_Capacity(SeqQueue* queue) // O(1)
{
TSeqQueue* sQueue = (TSeqQueue*)queue;
int ret = -1;
if( sQueue != NULL )
{
ret = sQueue->capacity;
}
return ret;
}
三、main.c
#include <stdio.h>
#include <stdlib.h>
#include "SeqQueue.h"
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
int main(int argc, char *argv[])
{
SeqQueue* queue = SeqQueue_Create(6);
int a[10] = {0};
int i = 0;
for(i=0; i<10; i++)
{
a[i] = i + 1;
SeqQueue_Append(queue, a + i);
}
printf("Header: %d\n", *(int*)SeqQueue_Header(queue));
printf("Length: %d\n", SeqQueue_Length(queue));
printf("Capacity: %d\n", SeqQueue_Capacity(queue));
while( SeqQueue_Length(queue) > 0 )
{
printf("Retrieve: %d\n", *(int*)SeqQueue_Retrieve(queue));
}
printf("\n");
for(i=0; i<10; i++)
{
a[i] = i + 1;
SeqQueue_Append(queue, a + i);
printf("Retrieve: %d\n", *(int*)SeqQueue_Retrieve(queue));
}
SeqQueue_Destroy(queue);
return 0;
}