标签：增加 有一个 loop 在线 实现 src 线性 -- char
之前实现的顺序栈和链式栈的进栈和出栈操作时间复杂度都是O(1)。而用同样的方式实现队列，进队和出队的复杂度总有一个是O(n) 。
顺序队列的瓶颈
顺序队列
线性表的第一个元素作为队头
线性表的最后一个元素作为队尾
入队的新元素是在线性表的最后，时间复杂度为O(1)；
出队时需要将后续的所有元素向前移动，时间复杂度为O(n)；
顺序队列的优化方案
定义顺序队列的头：
typedef unsigned int TSeqQueueNode; typedef struct _tag_SeqQueue { int capacity; int length; int front; int rear; TSeqQueueNode* node; } TSeqQueue;
顺序队列的创建
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; }
入队列
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); if( ret ) { sQueue->node[sQueue->rear] = (TSeqQueueNode)item; sQueue->rear = (sQueue->rear + 1) % sQueue->capacity; sQueue->length++; } return ret; }
出队列
void* SeqQueue_Retrieve(SeqQueue* queue) // O(1) { TSeqQueue* sQueue = (TSeqQueue*)queue; void* ret = SeqQueue_Header(queue); if( ret != NULL ) { sQueue->front = (sQueue->front + 1) % sQueue->capacity; sQueue->length--; } 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; }
出队列由原来的O(n)变成的O(1)；
完整版seqQueue.c代码：
#include <stdio.h> #include <malloc.h> #include "SeqQueue.h" typedef unsigned int TSeqQueueNode; typedef struct _tag_SeqQueue { int capacity; int length; int front; int rear; 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) // O(1) { TSeqQueue* sQueue = (TSeqQueue*)queue; if( sQueue != NULL ) { 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); if( ret ) { sQueue->node[sQueue->rear] = (TSeqQueueNode)item; sQueue->rear = (sQueue->rear + 1) % sQueue->capacity; sQueue->length++; } return ret; } void* SeqQueue_Retrieve(SeqQueue* queue) // O(1) { TSeqQueue* sQueue = (TSeqQueue*)queue; void* ret = SeqQueue_Header(queue); if( ret != NULL ) { sQueue->front = (sQueue->front + 1) % sQueue->capacity; sQueue->length--; } 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; }
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; }
运行结果为：
同样的，我们来实现链式队列；
链式队列的头：
typedef struct _tag_LinkQueue { TLinkQueueNode* front; TLinkQueueNode* rear; int length; } TLinkQueue;
节点：
struct _tag_LinkQueueNode { TLinkQueueNode* next; void* item; };
创建：
LinkQueue* LinkQueue_Create() // O(1) { TLinkQueue* ret = (TLinkQueue*)malloc(sizeof(TLinkQueue)); if( ret != NULL ) { ret->front = NULL; ret->rear = NULL; ret->length = 0; } return ret; }
入队列：
int LinkQueue_Append(LinkQueue* queue, void* item) // O(1) { TLinkQueue* sQueue = (TLinkQueue*)queue; TLinkQueueNode* node = (TLinkQueueNode*)malloc(sizeof(TLinkQueueNode)); int ret = (sQueue != NULL ) && (item != NULL) && (node != NULL); if( ret ) { node->item = item; if( sQueue->length > 0 ) { sQueue->rear->next = node; sQueue->rear = node; node->next = NULL; } else { sQueue->front = node; sQueue->rear = node; node->next = NULL; } sQueue->length++; } if( !ret ) { free(node); } return ret; }
出队列：
void* LinkQueue_Retrieve(LinkQueue* queue) // O(1) { TLinkQueue* sQueue = (TLinkQueue*)queue; TLinkQueueNode* node = NULL; void* ret = NULL; if( (sQueue != NULL) && (sQueue->length > 0) ) { node = sQueue->front; sQueue->front = node->next; ret = node->item; free(node); sQueue->length--; if( sQueue->length == 0 ) { sQueue->front = NULL; sQueue->rear = NULL; } } return ret; }
main.c
#include <stdio.h> #include <stdlib.h> #include "LinkQueue.h" /* run this program using the console pauser or add your own getch, system("pause") or input loop */ int main(int argc, char *argv[]) { LinkQueue* queue = LinkQueue_Create(); int a[10] = {0}; int i = 0; for(i=0; i<10; i++) { a[i] = i + 1; LinkQueue_Append(queue, a + i); } printf("Header: %d\n", *(int*)LinkQueue_Header(queue)); printf("Length: %d\n", LinkQueue_Length(queue)); // LinkQueue_Clear(queue); while( LinkQueue_Length(queue) > 0 ) { printf("Retrieve: %d\n", *(int*)LinkQueue_Retrieve(queue)); } LinkQueue_Destroy(queue); return 0; }
运行结果：
优化后的队列，增加了front，rear后，入队和出队都是O(1)；
标签：增加 有一个 loop 在线 实现 src 线性 -- char
原文地址：https://www.cnblogs.com/Liu-Jing/p/9574572.html
