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前言

一、棧

1.1 棧的概念結(jié)構(gòu)

棧也是一種線性表，數(shù)據(jù)在邏輯上挨著存儲(chǔ)。只允許在固定的一端進(jìn)行插入和刪除元素。進(jìn)行插入和刪除操作的一端叫棧頂，另一端叫棧底。符合LIFO 先進(jìn)后出。

壓棧：插入操作。
出棧：刪除操作。

1.2棧的實(shí)現(xiàn)

棧的實(shí)現(xiàn)用數(shù)組實(shí)現(xiàn)更好，因?yàn)橥昝婪蠑?shù)組的尾插尾刪。
數(shù)組的緩存利用率高一點(diǎn)。

小練習(xí)：

支持動(dòng)態(tài)增長的棧:

typedef int STDataType;
typedef struct Stack
{STDataType* _a;int _top; // 棧頂int _capacity; // 容量
}Stack;

初始化棧:

void StackInit(ST* ps)
{assert(ps);ps->a = NULL;ps->top = ps->capacity = 0;
}

入棧:進(jìn)棧（棧的插入操作），若棧未滿，則將x加入使之成為新棧頂。

void StackPush(ST* ps, STDataType x)
{assert(ps);if (ps->top == ps->capacity){int newCapacity = ps->capacity == 0 ? 4 : ps->capacity * 2;STDataType* tmp = (STDataType*)realloc(ps->a, newCapacity * sizeof(STDataType));if (tmp == NULL){perror("realloc fail");exit(-1);}ps->a = tmp;ps->capacity = newCapacity;}ps->a[ps->top] = x;ps->top++;
}

出棧:出棧（棧的刪除操作），若棧非空，則彈出棧頂元素，并用x返回。

void StackPop(ST* ps)
{assert(ps);assert(!StackEmpty(ps));--ps->top;
}

獲取棧頂元素:

STDataType StackTop(ST* ps)
{assert(ps);assert(!StackEmpty(ps));return ps->a[ps->top - 1];
}

獲取棧中有效元素個(gè)數(shù):

int StackSize(ST* ps)
{assert(ps);return ps->top;
}

銷毀棧:棧銷毀，并釋放占用的存儲(chǔ)空間

void StackDestroy(ST* ps)
{assert(ps);free(ps->a);ps->a = NULL;ps->capacity = ps->top = 0;
}

檢測棧是否為空，如果為空返回非零結(jié)果，如果不為空返回0:

bool StackEmpty(ST* ps)
{assert(ps);return ps->top == 0;
}

Stack.h

#pragma once
#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
#include<stdbool.h>
typedef int STDataType;
typedef struct Stack
{STDataType* a;int top;int capacity;
}ST;void StackInit(ST* ps);
void StackDestroy(ST* ps);
void StackPush(ST* ps, STDataType x);
void StackPop(ST* ps);
STDataType StackTop(ST* ps);
bool StackEmpty(ST* ps);
int StackSize(ST* ps);

Stack.c

#include "Stack.h"void StackInit(ST* ps)
{assert(ps);ps->a = NULL;ps->top = ps->capacity = 0;
}void StackDestroy(ST* ps)
{assert(ps);free(ps->a);ps->a = NULL;ps->capacity = ps->top = 0;
}void StackPush(ST* ps, STDataType x)
{assert(ps);if (ps->top == ps->capacity){int newCapacity = ps->capacity == 0 ? 4 : ps->capacity * 2;STDataType* tmp = (STDataType*)realloc(ps->a, newCapacity * sizeof(STDataType));if (tmp == NULL){perror("realloc fail");exit(-1);}ps->a = tmp;ps->capacity = newCapacity;}ps->a[ps->top] = x;ps->top++;
}void StackPop(ST* ps)
{assert(ps);assert(!StackEmpty(ps));--ps->top;
}STDataType StackTop(ST* ps)
{assert(ps);assert(!StackEmpty(ps));return ps->a[ps->top - 1];
}bool StackEmpty(ST* ps)
{assert(ps);return ps->top == 0;
}int StackSize(ST* ps)
{assert(ps);return ps->top;
}

二、隊(duì)列

2.1隊(duì)列的概念及結(jié)構(gòu)

隊(duì)列：只允許在一端進(jìn)行插入數(shù)據(jù)操作，在另一端進(jìn)行刪除數(shù)據(jù)操作的特殊線性表，隊(duì)列具有先進(jìn)先出FIFO(First In First Out)
入隊(duì)列：進(jìn)行插入操作的一端稱為隊(duì)尾。
出隊(duì)列：進(jìn)行刪除操作的一端稱為隊(duì)頭。

2.2隊(duì)列的實(shí)現(xiàn)

隊(duì)列用鏈表的結(jié)構(gòu)實(shí)現(xiàn)更優(yōu)

鏈?zhǔn)浇Y(jié)構(gòu)：表示隊(duì)列

typedef struct QListNode
{ struct QListNode* _pNext; QDataType _data; 
}QNode;

隊(duì)列的結(jié)構(gòu)：

typedef struct Queue
{QNode* head;QNode* tail;int size;
}Queue;

初始化隊(duì)列：

void QueueInit(Queue* pq)
{assert(pq);pq->head = pq->tail = NULL;pq->size = 0;
}

隊(duì)尾入隊(duì)列：

void QueuePush(Queue* pq, QDataType x)
{assert(pq);QNode* newnode = (QNode*)malloc(sizeof(QNode));if (newnode == NULL){perror("malloc fail");exit(-1);}else{newnode->data = x;newnode->next = NULL;}if (pq->tail == NULL){pq->head = pq->tail = newnode;}else{pq->tail->next = newnode;pq->tail = newnode;}pq->size++;
}

隊(duì)頭出隊(duì)列：

void QueuePop(Queue* pq)
{assert(pq);assert(!QueueEmpty(pq));if (pq->head->next == NULL){free(pq->head);pq->head = pq->tail = NULL;}else{QNode* del = pq->head;pq->head = pq->head->next;free(del);del = NULL;}pq->size--;
}

獲取隊(duì)列頭部元素：

QDataType QueueFront(Queue* pq)
{assert(pq);assert(!QueueEmpty(pq));return pq->head->data;
}

獲取隊(duì)列隊(duì)尾元素：

QDataType QueueBack(Queue* pq)
{assert(pq);assert(!QueueEmpty(pq));return pq->tail->data;
}

獲取隊(duì)列中有效元素個(gè)數(shù)：

int QueueSize(Queue* pq)
{assert(pq);return pq->size;
}

檢測隊(duì)列是否為空，如果為空返回非零結(jié)果，如果非空返回0：

bool QueueEmpty(Queue* pq)
{assert(pq);return pq->head == NULL && pq->tail == NULL;
}

銷毀隊(duì)列：

void QueueDestroy(Queue* pq)
{assert(pq);QNode* cur = pq->head;while (cur){QNode* del = cur;cur = cur->next;free(del);}pq->head = pq->tail = NULL;
}

Queue.h

#pragma once
#include <stdio.h>
#include<stdlib.h>
#include<assert.h>
#include<stdbool.h>typedef int QDataType;
typedef struct QueueNode
{struct QueueNode* next;QDataType data;
}QNode;typedef struct Queue
{QNode* head;QNode* tail;int size;
}Queue;void QueueInit(Queue* pq);
void QueueDestroy(Queue* pq);
void QueuePush(Queue* pq, QDataType x);
QDataType QueueFront(Queue* pq);
QDataType QueueBack(Queue* pq);
bool QueueEmpty(Queue* pq);
int QueueSize(Queue* pq);

Queue.c

#include"Queue.h"void QueueInit(Queue* pq)
{assert(pq);pq->head = pq->tail = NULL;pq->size = 0;
}void QueueDestroy(Queue* pq)
{assert(pq);QNode* cur = pq->head;while (cur){QNode* del = cur;cur = cur->next;free(del);}pq->head = pq->tail = NULL;
}void QueuePush(Queue* pq, QDataType x)
{assert(pq);QNode* newnode = (QNode*)malloc(sizeof(QNode));if (newnode == NULL){perror("malloc fail");exit(-1);}else{newnode->data = x;newnode->next = NULL;}if (pq->tail == NULL){pq->head = pq->tail = newnode;}else{pq->tail->next = newnode;pq->tail = newnode;}pq->size++;
}void QueuePop(Queue* pq)
{assert(pq);assert(!QueueEmpty(pq));if (pq->head->next == NULL){free(pq->head);pq->head = pq->tail = NULL;}else{QNode* del = pq->head;pq->head = pq->head->next;free(del);del = NULL;}pq->size--;
}QDataType QueueFront(Queue* pq)
{assert(pq);assert(!QueueEmpty(pq));return pq->head->data;
}QDataType QueueBack(Queue* pq)
{assert(pq);assert(!QueueEmpty(pq));return pq->tail->data;
}bool QueueEmpty(Queue* pq)
{assert(pq);return pq->head == NULL && pq->tail == NULL;
}int QueueSize(Queue* pq)
{assert(pq);return pq->size;
}

三、棧和隊(duì)列面試題

題目鏈接：
1.https://leetcode.cn/problems/valid-parentheses/

題目鏈接：
2.https://leetcode.cn/problems/implement-stack-using-queues/

總結(jié)