数据结构面试例题：括号匹配、栈实现队列、队列实现栈，循坏队列（C语言解决）

hello,这次我来用C语言和栈和队列相关问题，希望大家多多支持

括号匹配题目：

OJ题目

首先我们不能用数量匹配来进行解答，因为你顺序不一定匹配

解析：

1、左括号入栈

2、右括号出栈顶左括号匹配

1.我们只需要找到右括号，判断左括号是否匹配

2、所以遇到左括号就采用进入栈的方式，遇到右括号，出栈顶左括号看是否匹配

cpp 复制代码

typedef char 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);
int StackSize(ST* ps);
bool StackEmpty(ST* ps);

void StackInit(ST* ps)
{
	assert(ps);
	ps->a = NULL;
	ps->top = 0;//ps->top = -1
	ps->capacity = 0;
}


void StackDestroy(ST* ps)
{
	assert(ps);
	free(ps->a);
	ps->a = NULL;
	ps->top = ps->capacity = 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 = realloc(ps->a, sizeof(STDataType) * newCapacity);
		if (tmp == NULL)
		{
			printf("realloc fail\n");
			exit(-1);
		}

		ps->a = tmp;
		ps->capacity = newCapacity;
	}

	ps->a[ps->top] = x;
	ps->top++;
}


void StackPop(ST* ps)
{
	assert(ps);
	//assert(ps->top > 0);
	assert(!StackEmpty(ps));

	ps->top--;
}

STDataType StackTop(ST* ps)
{
	assert(ps);
	//assert(ps->top > 0);
	assert(!StackEmpty(ps));

	return ps->a[ps->top - 1];
}

int StackSize(ST* ps)
{
	assert(ps);

	return ps->top;
}


bool StackEmpty(ST* ps)
{
	assert(ps);

	return ps->top == 0;
}

bool isValid(char* s) 
{
    ST st;
    StackInit(&st);
    while(*s)
    {
        if (*s == '(' 
        || *s == '{' 
        || *s == '[')
        {
            StackPush(&st, *s);
            ++s;
        }
        else
        {
         
            if (StackEmpty(&st))
            {
                StackDestroy(&st);
                return false;
            }

            STDataType top = StackTop(&st);
            StackPop(&st);
            if ((*s == '}' && top != '{')
            || (*s == ']' && top != '[')
            || (*s == ')' && top != '('))
            {
                StackDestroy(&st);
                return false;
            }
            else
            {
                s++;
            }
        }
    }


    bool ret = StackEmpty(&st);
    StackDestroy(&st);
    return ret;
}

用队列实现栈

OJ题目https://leetcode.cn/problems/implement-stack-using-queues/description/

我们知道队列是先进先出，栈是先进后出（后入先出）

1、我们主要保证一个队列是空，然后把这个队列数据存入另外一个队列中，这个时候的队列所出的数据相当于就是栈出的数据。

2、所以插入数据是插到有数据的队列，如果两个都没有数据两个都行。

cpp 复制代码

typedef struct {
    Queue q1;
    Queue q2;
    
} MyStack;

/** Initialize your data structure here. */
MyStack* myStackCreate(int maxSize) {
    MyStack* pst = (MyStack*)malloc(sizeof(MyStack));
    QueueInit(&pst->q1);
    QueueInit(&pst->q2);
        
    return pst;
}

/** Push element x onto stack. */
void myStackPush(MyStack* obj, int x) {
    //给非空队列进行入队操作
    if(QueueEmpty(&obj->q1) != 0)
    {
        QueuePush(&obj->q1, x);
    }
    else
    {
        QueuePush(&obj->q2, x);
    }
}

/** Removes the element on top of the stack and returns that element. */
int myStackPop(MyStack* obj) {
    //把非空队列的除最后一个元素之外的剩余元素全部入队空队列
    Queue* pEmpty = &obj->q1, *pNonEmpty = &obj->q2;
    if(QueueEmpty(&obj->q1) != 0)
    {
        pEmpty = &obj->q2;
        pNonEmpty = &obj->q1;
    }
    
    while(QueueSize(pNonEmpty) > 1)
    {
        QueuePush(pEmpty, QueueFront(pNonEmpty));
        QueuePop(pNonEmpty);
    }
    
    int top = QueueFront(pNonEmpty);
    //队尾元素出队
    QueuePop(pNonEmpty);
    
    return top;
}

/** Get the top element. */
int myStackTop(MyStack* obj) {
    //获取非空队列的队尾元素
    Queue* pEmpty = &obj->q1, *pNonEmpty = &obj->q2;
    if(QueueEmpty(&obj->q1) != 0)
    {
        pEmpty = &obj->q2;
        pNonEmpty = &obj->q1;
    }
    
    return QueueBack(pNonEmpty);
}

/** Returns whether the stack is empty. */
bool myStackEmpty(MyStack* obj) {
    return !(QueueEmpty(&obj->q1) | QueueEmpty(&obj->q2));
}

void myStackFree(MyStack* obj) {
    QueueDestory(&obj->q1);
    QueueDestory(&obj->q2);
    free(obj);
}

用栈实现队列

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

cpp 复制代码

typedef struct {
    //入队栈
    Stack pushST;
    //出队栈
    Stack popST;
} MyQueue;

/** Initialize your data structure here. */
MyQueue* myQueueCreate(int maxSize) {
    MyQueue* pqueue = (MyQueue*)malloc(sizeof(MyQueue));
    StackInit(&pqueue->pushST, maxSize);
    StackInit(&pqueue->popST, maxSize);
    return pqueue;
}

/** Push element x to the back of queue. */
void myQueuePush(MyQueue* obj, int x) {
    //入队栈进行入栈操作
    StackPush(&obj->pushST, x);
}

/** Removes the element from in front of queue and returns that element. */
int myQueuePop(MyQueue* obj) {
    //如果出队栈为空，导入入队栈的元素
    if(StackEmpty(&obj->popST) == 0)
    {
        while(StackEmpty(&obj->pushST) != 0)
        {
            StackPush(&obj->popST, StackTop(&obj->pushST));
            StackPop(&obj->pushST);
        }
    }
    
    int front = StackTop(&obj->popST);
    //出队栈进行出队操作
    StackPop(&obj->popST);
    return front;
}

/** Get the front element. */
int myQueuePeek(MyQueue* obj) {
    //类似于出队操作
    if(StackEmpty(&obj->popST) == 0)
    {
        while(StackEmpty(&obj->pushST) != 0)
        {
            StackPush(&obj->popST, StackTop(&obj->pushST));
            StackPop(&obj->pushST);
        }
    }
    
    return StackTop(&obj->popST);
}

/** Returns whether the queue is empty. */
bool myQueueEmpty(MyQueue* obj) {
    return StackEmpty(&obj->pushST) == 0
        &&  StackEmpty(&obj->popST) == 0;
}

void myQueueFree(MyQueue* obj) {
    StackDestroy(&obj->pushST);
    StackDestroy(&obj->popST);
    
    free(obj);
}

设计循坏队列

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

cpp 复制代码

typedef struct {
    int* queue;
    int front;
    int rear;
    int k
} MyCircularQueue;

/** Initialize your data structure here. Set the size of the queue to be k. */
//创建一个可以存放k个元素的循环队列，实际申请的空间为k + 1
MyCircularQueue* myCircularQueueCreate(int k) {
    MyCircularQueue* pcq = (MyCircularQueue*)malloc(sizeof(MyCircularQueue));
    pcq->queue = (int*)malloc(sizeof(int)*(k+1));
    pcq->front = 0;
    pcq->rear = 0;
    pcq->k = k;
    
    return pcq;
}

/** Insert an element into the circular queue. Return true if the operation is successful. */
bool myCircularQueueEnQueue(MyCircularQueue* obj, int value) {
    //判满
    if((obj->rear+1)%(obj->k+1) == obj->front)
    {
        return false;
    }
    //队尾入队
    obj->queue[obj->rear++] = value;
    //如果队尾越界，更新为最小值
    if(obj->rear == obj->k+1)
        obj->rear = 0;
    
    return true;
}

/** Delete an element from the circular queue. Return true if the operation is successful. */
bool myCircularQueueDeQueue(MyCircularQueue* obj) {
    //判空
    if(obj->front == obj->rear)
        return false;
    //队头出队
    ++obj->front;
    //如果队头越界，更新为最小值
    if(obj->front == obj->k+1)
        obj->front = 0;
    
    return true;
}

/** Get the front item from the queue. */
int myCircularQueueFront(MyCircularQueue* obj) {
    if(obj->front == obj->rear)
        return -1;
    else
        return obj->queue[obj->front];
}

/** Get the last item from the queue. */
int myCircularQueueRear(MyCircularQueue* obj) {
     if(obj->front == obj->rear)
        return -1;
    //队尾元素再rear索引的前一个位置，如果rear为0，
    //则队尾元素在数组的最后一个位置
    if(obj->rear == 0)
        return obj->queue[obj->k];
    else
        return obj->queue[obj->rear-1];
}

/** Checks whether the circular queue is empty or not. */
bool myCircularQueueIsEmpty(MyCircularQueue* obj) {
    return obj->front == obj->rear;
}

/** Checks whether the circular queue is full or not. */
bool myCircularQueueIsFull(MyCircularQueue* obj) {
    return (obj->rear+1)%(obj->k+1) == obj->front;
}

void myCircularQueueFree(MyCircularQueue* obj) {
    free(obj->queue);
    free(obj);
}

一些解析都在代码里啦

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