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栈的定义

栈：一种特殊的线性表，其只允许在固定的一端进行插入和删除元素操作。进行数据插入和删除操作的一端称为栈顶，另一端称为栈底。栈中的数据元素遵守后进先出LIFO（Last In First Out）的原则。
压栈：栈的插入操作叫做进栈/压栈/入栈，入数据在栈顶。
出栈：栈的删除操作叫做出栈。出数据也在栈顶
可以把他想象成一个水杯

栈代码的实现

结构的定义，以及函数声明

#pragma once
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <stdbool.h>typedef int QueueNodeType;
struct QueueNode {struct QueueNode* next;QueueNodeType data;
}typedef QueueNode;//队列只需要在队尾插入，队头删除，不需要改变里面的内容
//所以只需要改变头尾
struct Queue {struct QueueNode* head;struct QueueNode* tail;size_t _size;
}typedef Queue;// 初始化队列
void QueueInit(Queue* q);
// 队尾入队列
void QueuePush(Queue* q, QueueNodeType data);
// 队头出队列
void QueuePop(Queue* q);
// 获取队列头部元素
QueueNodeType QueueFront(Queue* q);
// 获取队列队尾元素
QueueNodeType QueueBack(Queue* q);
// 获取队列中有效元素个数
size_t QueueSize(Queue* q);
// 检测队列是否为空，如果为空返回非零结果，如果非空返回0 
bool QueueEmpty(Queue* q);
// 销毁队列
void QueueDestroy(Queue* q);

接口的实现

#define  _CRT_SECURE_NO_WARNINGS 1
#include "queue.h"void QueueInit(Queue* q)
{assert(q);q->head = NULL;q->tail = NULL;q->_size = 0;
}void QueueDestroy(Queue* q)
{assert(q);while (q->head){QueueNode* next = q->head->next;free(q->head);q->head = next;}q->tail = NULL;q->_size = 0;
}void QueuePush(Queue* q, QueueNodeType data)
{assert(q);QueueNode* newnode = (QueueNode*)malloc(sizeof(QueueNode));assert(newnode);newnode->data = data;newnode->next = NULL;//尾插if (q->tail == NULL){q->tail = q->head = newnode;}else{q->tail->next = newnode;q->tail = q->tail->next;}q->_size++;
}void QueuePop(Queue* q)
{assert(q);assert(!QueueEmpty(q));QueueNode* newhead = q->head->next;free(q->head);q->head = newhead;if (q->head == NULL){q->tail = NULL;}q->_size--;
}bool QueueEmpty(Queue* q)
{assert(q);return q->head == NULL;
}QueueNodeType QueueFront(Queue* q)
{assert(q);assert(!QueueEmpty(q));return q->head->data;
}QueueNodeType QueueBack(Queue* q)
{assert(q);assert(!QueueEmpty(q));return q->tail->data;
}size_t QueueSize(Queue* q)
{assert(q);return q->_size;
}

队列的定义

队列：只允许在一端进行插入数据操作，在另一端进行删除数据操作的特殊线性表，队列具有先进先出FIFO(First In First Out)
入队列：进行插入操作的一端称为队尾
出队列：进行删除操作的一端称为队头

队列代码的实现

结构的定义，以及函数声明

#pragma once
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <stdbool.h>typedef int QueueNodeType;
struct QueueNode {struct QueueNode* next;QueueNodeType data;
}typedef QueueNode;//队列只需要在队尾插入，队头删除，不需要改变里面的内容
//所以只需要改变头尾
struct Queue {struct QueueNode* head;struct QueueNode* tail;size_t _size;
}typedef Queue;// 初始化队列
void QueueInit(Queue* q);
// 队尾入队列
void QueuePush(Queue* q, QueueNodeType data);
// 队头出队列
void QueuePop(Queue* q);
// 获取队列头部元素
QueueNodeType QueueFront(Queue* q);
// 获取队列队尾元素
QueueNodeType QueueBack(Queue* q);
// 获取队列中有效元素个数
size_t QueueSize(Queue* q);
// 检测队列是否为空，如果为空返回非零结果，如果非空返回0 
bool QueueEmpty(Queue* q);
// 销毁队列
void QueueDestroy(Queue* q);

接口的实现

#define  _CRT_SECURE_NO_WARNINGS 1
#include "queue.h"void QueueInit(Queue* q)
{assert(q);q->head = NULL;q->tail = NULL;q->_size = 0;
}void QueueDestroy(Queue* q)
{assert(q);while (q->head){QueueNode* next = q->head->next;free(q->head);q->head = next;}q->tail = NULL;q->_size = 0;
}void QueuePush(Queue* q, QueueNodeType data)
{assert(q);QueueNode* newnode = (QueueNode*)malloc(sizeof(QueueNode));assert(newnode);newnode->data = data;newnode->next = NULL;//尾插if (q->tail == NULL){q->tail = q->head = newnode;}else{q->tail->next = newnode;q->tail = q->tail->next;}q->_size++;
}void QueuePop(Queue* q)
{assert(q);assert(!QueueEmpty(q));QueueNode* newhead = q->head->next;free(q->head);q->head = newhead;if (q->head == NULL){q->tail = NULL;}q->_size--;
}bool QueueEmpty(Queue* q)
{assert(q);return q->head == NULL;
}QueueNodeType QueueFront(Queue* q)
{assert(q);assert(!QueueEmpty(q));return q->head->data;
}QueueNodeType QueueBack(Queue* q)
{assert(q);assert(!QueueEmpty(q));return q->tail->data;
}size_t QueueSize(Queue* q)
{assert(q);return q->_size;
}

题目1：括号匹配问题

题目链接：https://leetcode.cn/problems/valid-parentheses/description/

思路详解：

参考代码

typedef char StackType;struct Stack {StackType* _a;int _top;int _capacity;
}typedef Stack;//初始化栈
void StackInit(Stack* pStack);//入栈
void StackPush(Stack* pStack,StackType data);//出栈
void StackPop(Stack* pStack);//获取栈顶元素
StackType StackTop(const Stack* pStack);//获取栈中有效元素个数
int StackSize(const Stack* pStack);//判断栈是否为空
bool StackEmpty(Stack* pStack);//销毁栈
void StackDestroy(Stack* pStack);void StackInit(Stack* pStack)
{pStack->_a = NULL;pStack->_capacity = 0;pStack->_top = 0;
}void StackPush(Stack* pStack,StackType data)
{assert(pStack);if (pStack->_top == pStack->_capacity){int newCapacity = pStack->_capacity == 0 ? 4 : pStack->_capacity * 2;StackType* newa = NULL;newa = (StackType*)realloc(pStack->_a, sizeof(StackType) * newCapacity);if (newa == NULL){perror("StackPush():: realloc::");return;}pStack->_a = newa;pStack->_capacity = newCapacity;}pStack->_a[pStack->_top] = data;pStack->_top++;
}void StackPop(Stack* pStack)
{assert(pStack);assert(!StackEmpty(pStack));pStack->_top--;
}StackType StackTop(const Stack* pStack)
{// 因为top的初始值为0 ，而插入一个数据后为1，// 但是所对应的数组下标为0assert(pStack);assert(!StackEmpty(pStack));return pStack->_a[pStack->_top - 1];
}int StackSize(const Stack* pStack)
{return pStack->_top;
}bool StackEmpty(Stack* pStack)
{assert(pStack);return pStack->_top == 0;
}void StackDestroy(Stack* pStack)
{free(pStack->_a);pStack->_capacity = 0;pStack->_top = 0;pStack->_a = NULL;
}
//这里题目实现，上面都是栈的实现和接口，因为是C语言的关系没有STL库所以要自己造轮子
bool isValid(char* s) 
{Stack stack = { 0 };StackInit(&stack);while (*s){if (*s == '(' || *s == '{' || *s == '['){StackPush(&stack, *s);s++;}else{//第一个字符为有括号，证明不是有效括号，直接返回NULLif(StackEmpty(&stack)){//特殊案例如果是 [[]]],这里如果直接返回的话就会导致内存泄露StackDestroy(&stack);return false;}StackType top = StackTop(&stack);StackPop(&stack);if (top == '(' && *s != ')'|| top == '{' && *s != '}'|| top == '[' && *s != ']'){StackDestroy(&stack);return false;}else{ s++;}}}bool ret = StackEmpty(&stack);StackDestroy(&stack);return ret;// return true;
}

题目2：用队列实现栈

题目链接：https://leetcode.cn/problems/implement-stack-using-queues/

思路详解：

参考代码：

typedef int QueueNodeType;
struct QueueNode {struct QueueNode* next;QueueNodeType data;
}typedef QueueNode;//队列只需要在队尾插入，队头删除，不需要改变里面的内容
//所以只需要改变头尾
struct Queue {struct QueueNode* head;struct QueueNode* tail;size_t _size;
}typedef Queue;// 初始化队列
void QueueInit(Queue* q);
// 队尾入队列
void QueuePush(Queue* q, QueueNodeType data);
// 队头出队列
void QueuePop(Queue* q);
// 获取队列头部元素
QueueNodeType QueueFront(Queue* q);
// 获取队列队尾元素
QueueNodeType QueueBack(Queue* q);
// 获取队列中有效元素个数
size_t QueueSize(Queue* q);
// 检测队列是否为空，如果为空返回非零结果，如果非空返回0 
bool QueueEmpty(Queue* q);
// 销毁队列
void QueueDestroy(Queue* q);void QueueInit(Queue* q)
{assert(q);q->head = NULL;q->tail = NULL;q->_size = 0;
}void QueueDestroy(Queue* q)
{assert(q);while (q->head){QueueNode* next = q->head->next;free(q->head);q->head = next;}q->tail = NULL;q->_size = 0;
}void QueuePush(Queue* q, QueueNodeType data)
{assert(q);QueueNode* newnode = (QueueNode*)malloc(sizeof(QueueNode));assert(newnode);newnode->data = data;newnode->next = NULL;//尾插if (q->tail == NULL){q->tail = q->head = newnode;}else{q->tail->next = newnode;q->tail = q->tail->next;}q->_size++;
}void QueuePop(Queue* q)
{assert(q);assert(!QueueEmpty(q));QueueNode* newhead = q->head->next;free(q->head);q->head = newhead;if (q->head == NULL){q->tail = NULL;}q->_size--;
}bool QueueEmpty(Queue* q)
{assert(q);return q->head == NULL;
}QueueNodeType QueueFront(Queue* q)
{assert(q);assert(!QueueEmpty(q));return q->head->data;
}QueueNodeType QueueBack(Queue* q)
{assert(q);assert(!QueueEmpty(q));return q->tail->data;
}size_t QueueSize(Queue* q)
{assert(q);return q->_size;
}//上面是队列的接口，从这里下面才开始对栈的实现
typedef struct {Queue q1;Queue q2;
} MyStack;MyStack* myStackCreate() {MyStack* mystack = (MyStack*)malloc(sizeof(MyStack));QueueInit(&mystack->q1);QueueInit(&mystack->q2);return mystack;
}void myStackPush(MyStack* obj, int x) {if(QueueEmpty(&obj->q1)){QueuePush(&obj->q2,x);}else{QueuePush(&obj->q1,x);}
}int myStackPop(MyStack* obj) {//找那个是为空队列Queue* emptyQueue = &obj->q1;Queue* nonEmptyQueue = &obj->q2;if(QueueEmpty(&obj->q2)){emptyQueue = &obj->q2;nonEmptyQueue = &obj->q1;}//保留非空队列中的最后一个元素，其余元素转移到空队列里面while(QueueSize(nonEmptyQueue) > 1){QueuePush(emptyQueue,QueueFront(nonEmptyQueue));QueuePop(nonEmptyQueue);}int ret = QueueFront(nonEmptyQueue);QueuePop(nonEmptyQueue);return ret;
}int myStackTop(MyStack* obj) {//两个队列中，非空的那个队列的队尾就是栈顶if(QueueEmpty(&obj->q1)){return QueueBack(&obj->q2); }else{return QueueBack(&obj->q1);}
}bool myStackEmpty(MyStack* obj) {return QueueEmpty(&obj->q1) && QueueEmpty(&obj->q2);
}void myStackFree(MyStack* obj) {QueueDestroy(&obj->q1);QueueDestroy(&obj->q2);free(obj);
}

题目3：用栈实现队列

题目链接：https://leetcode.cn/problems/implement-queue-using-stacks/description/

思路详解：

参考代码：

typedef char StackType;struct Stack {StackType* _a;int _top;int _capacity;
}typedef Stack;//初始化栈
void StackInit(Stack* pStack);//入栈
void StackPush(Stack* pStack,StackType data);//出栈
void StackPop(Stack* pStack);//获取栈顶元素
StackType StackTop(Stack* pStack);//获取栈底元素
StackType StackBottom(Stack* pStack);//获取栈中有效元素个数
int StackSize(Stack* pStack);//判断栈是否为空
bool StackEmpty(Stack* pStack);//销毁栈
void StackDestroy(Stack* pStack);void StackInit(Stack* pStack)
{pStack->_a = NULL;pStack->_capacity = 0;pStack->_top = 0;
}void StackPush(Stack* pStack,StackType data)
{assert(pStack);if (pStack->_top == pStack->_capacity){int newCapacity = pStack->_capacity == 0 ? 4 : pStack->_capacity * 2;StackType* newa = NULL;newa = (StackType*)realloc(pStack->_a, sizeof(StackType) * newCapacity);if (newa == NULL){perror("StackPush():: realloc::");return;}pStack->_a = newa;pStack->_capacity = newCapacity;}pStack->_a[pStack->_top] = data;pStack->_top++;
}void StackPop(Stack* pStack)
{assert(pStack);assert(!StackEmpty(pStack));pStack->_top--;
}StackType StackTop(Stack* pStack)
{assert(pStack);assert(!StackEmpty(pStack));// 因为top的初始值为0 ，而插入一个数据后为1，// 但是所对应的数组下标为0return pStack->_a[pStack->_top - 1];
}StackType StackBottom(Stack* pStack)
{assert(pStack);assert(!StackEmpty(pStack));return pStack->_a[0];
}int StackSize(Stack* pStack)
{return pStack->_top;
}bool StackEmpty(Stack* pStack)
{assert(pStack);return pStack->_top == 0;
}void StackDestroy(Stack* pStack)
{free(pStack->_a);pStack->_capacity = 0;pStack->_top = 0;pStack->_a = NULL;
}//这里开始才是实现队列的代码
typedef struct {Stack PushStack;Stack PopStack;
} MyQueue;MyQueue* myQueueCreate() {MyQueue* queue= (MyQueue*)malloc(sizeof(MyQueue));StackInit(&queue->PushStack);StackInit(&queue->PopStack);return queue;
}void myQueuePush(MyQueue* obj, int x) {StackPush(&obj->PushStack,x);
}int myQueuePop(MyQueue* obj) {if(StackEmpty(&obj->PopStack)){while(!StackEmpty(&obj->PushStack)){StackPush(&obj->PopStack,StackTop(&obj->PushStack));StackPop(&obj->PushStack);}}int popTop = StackTop(&obj->PopStack);StackPop(&obj->PopStack);return popTop;
}//返回队头
int myQueuePeek(MyQueue* obj) {if(StackEmpty(&obj->PopStack)){while(!StackEmpty(&obj->PushStack)){StackPush(&obj->PopStack,StackTop(&obj->PushStack));StackPop(&obj->PushStack);}}return StackTop(&obj->PopStack);
}bool myQueueEmpty(MyQueue* obj) {return StackEmpty(&obj->PushStack) && StackEmpty(&obj->PopStack);
}void myQueueFree(MyQueue* obj) {StackDestroy(&obj->PopStack);StackDestroy(&obj->PushStack);free(obj);
}

题目4：设计循环队列

题目链接：https://leetcode.cn/problems/design-circular-queue/description/

思路详解：

参考代码：
用数组实现：

typedef struct {int* _a; //数组int _head; //头下标int _tail; //尾下标int _k; //存储的元素个数
} MyCircularQueue;
bool myCircularQueueIsEmpty(MyCircularQueue* obj);
bool myCircularQueueIsFull(MyCircularQueue* obj);// 初始化
MyCircularQueue* myCircularQueueCreate(int k) {MyCircularQueue* cq = (MyCircularQueue*)malloc(sizeof(MyCircularQueue));assert(cq);cq->_a = (int*)malloc(sizeof(int) * (k + 1));assert(cq->_a);cq->_head = 0;cq->_tail = 0;cq->_k = k;return cq;
}// 入队列
bool myCircularQueueEnQueue(MyCircularQueue * obj, int value) {assert(obj);if (myCircularQueueIsFull(obj)){return false;}else{obj->_a[obj->_tail] = value;if (obj->_tail >= obj->_k){obj->_tail = 0;}else{obj->_tail++;}return true;}
}//删队列
bool myCircularQueueDeQueue(MyCircularQueue* obj) {assert(obj);if (myCircularQueueIsEmpty(obj)){return false;}if (obj->_head >= obj->_k){obj->_head = 0;return true;}else{obj->_head++;return true;}
}//队头
int myCircularQueueFront(MyCircularQueue* obj) {assert(obj);if (myCircularQueueIsEmpty(obj)){return -1; }return obj->_a[obj->_head];
}//队尾
int myCircularQueueRear(MyCircularQueue* obj) {assert(obj);if (myCircularQueueIsEmpty(obj)){return -1;}//方法1；if (obj->_tail == 0){return obj->_a[obj->_k];}else{return obj->_a[obj->_tail - 1];}//方法2：/*int i = (obj->_tail + obj->_k) % (obj->_k + 1);return obj->_a[i];*/
}//判空
bool myCircularQueueIsEmpty(MyCircularQueue* obj) {assert(obj);return obj->_head == obj->_tail;
}//判满
bool myCircularQueueIsFull(MyCircularQueue* obj) {assert(obj);return (obj->_tail + 1) % (obj->_k + 1) == obj->_head;
}//销毁
void myCircularQueueFree(MyCircularQueue* obj) {assert(obj);free(obj->_a);free(obj);
}