一、用队列实现栈
1、题目描述
https://leetcode.cn/problems/implement-stack-using-queues
2、算法分析
入栈：往不为空的队列中插入数据。
出栈：把不为空的队列中前size-1个数据挪到另一个队列中，再将最后一个数据出队。
取栈顶元素：取不为空队列中队尾结点的数据。
3、参考代码
cpp
typedef int QDataType;
//队列结点的结构
typedef struct QueueNode
{
QDataType data;
struct QueueNode* next;
}QueueNode;
//队列的结构
typedef struct Queue
{
QueueNode* phead;
QueueNode* ptail;
int size; //队列中有效数据个数
}Queue;
//初始化
void QueueInit(Queue* pq)
{
assert(pq);
pq->phead = pq->ptail = NULL;
pq->size = 0;
}
//销毁队列
void QueueDestroy(Queue* pq)
{
assert(pq);
QueueNode* pcur = pq->phead;
while (pcur)
{
QueueNode* next = pcur->next;
free(pcur);
pcur = next;
}
pq->phead = pq->ptail = NULL;
pq->size = 0;
}
//入队------队尾
void QueuePush(Queue* pq, QDataType x)
{
assert(pq);
QueueNode* newnode = (QueueNode*)malloc(sizeof(QueueNode));
if (newnode == NULL)
{
perror("malloc fail!");
exit(1);
}
newnode->data = x;
newnode->next = NULL;
//队列为空
if (pq->phead == NULL)
{
pq->phead = pq->ptail = newnode;
}
else
{
//队列非空
pq->ptail->next = newnode;
pq->ptail = pq->ptail->next;
}
pq->size++;
}
//队列判空
bool QueueEmpty(Queue* pq)
{
assert(pq);
return pq->phead == NULL;
}
//出队------队头
void QueuePop(Queue* pq)
{
assert(!QueueEmpty(pq));
//只有一个结点，phead和ptail都要置为空
if (pq->phead == pq->ptail)
{
free(pq->phead);
pq->phead = pq->ptail = NULL;
}
else
{
QueueNode* next = pq->phead->next;
free(pq->phead);
pq->phead = next;
}
pq->size--;
}
//取队头数据
QDataType QueueFront(Queue* pq)
{
assert(!QueueEmpty(pq));
return pq->phead->data;
}
//取队尾数据
QDataType QueueBack(Queue* pq)
{
assert(!QueueEmpty(pq));
return pq->ptail->data;
}
//队列有效元素个数
int QueueSize(Queue* pq)
{
assert(pq);
return pq->size;
}
/////////////////////////以上是队列结构和方法的实现/////////////////////
typedef struct
{
Queue q1;
Queue q2;
} MyStack;
MyStack* myStackCreate()
{
MyStack* pst = (MyStack*)malloc(sizeof(MyStack));
QueueInit(&pst->q1);
QueueInit(&pst->q2);
return pst;
}
void myStackPush(MyStack* obj, int x)
{
//往不为空的队列中插入数据
if(!QueueEmpty(&obj->q1))
{
QueuePush(&obj->q1, x);
}
else
{
QueuePush(&obj->q2, x);
}
}
int myStackPop(MyStack* obj)
{
//将不为空的队列中前size-1个数据挪到另一个队列中
//再将最后一个数据出队列
Queue* emp = &obj->q1;
Queue* nonEmp = &obj->q2;
if(QueueEmpty(&obj->q2))
{
nonEmp = &obj->q1;
emp = &obj->q2;
}
while(QueueSize(nonEmp) > 1)
{
int front = QueueFront(nonEmp);
QueuePush(emp, front);
QueuePop(nonEmp);
}
int top = QueueFront(nonEmp);
QueuePop(nonEmp);
return top;
}
//取栈顶
int myStackTop(MyStack* obj)
{
//找不为空队列中的队尾数据
if(!QueueEmpty(&obj->q1))
{
return QueueBack(&obj->q1);
}
else
{
return QueueBack(&obj->q2);
}
}
bool myStackEmpty(MyStack* obj)
{
return QueueEmpty(&obj->q1) && QueueEmpty(&obj->q2);
}
//销毁
void myStackFree(MyStack* obj)
{
QueueDestroy(&obj->q1);
QueueDestroy(&obj->q2);
free(obj);
obj = NULL;
}
/**
* Your MyStack struct will be instantiated and called as such:
* MyStack* obj = myStackCreate();
* myStackPush(obj, x);
* int param_2 = myStackPop(obj);
* int param_3 = myStackTop(obj);
* bool param_4 = myStackEmpty(obj);
* myStackFree(obj);
*/二、用栈实现队列
1、题目描述
https://leetcode.cn/problems/implement-queue-using-stacks
2、算法分析
入队：往pushST中插入数据。
出队：如果popST不为空，直接出数据；否则将popST中的数据导入到popST中再出数据。
取队头元素：逻辑同出队操作，但是这里只取数据，不删除数据。
3、参考代码
cpp
//定义栈的结构
typedef int STDataType;
typedef struct Stack
{
STDataType* arr;
int top; //指向栈顶的位置
int capacity; //栈的容量
}ST;
//初始化
void StackInit(ST* ps)
{
ps->arr = NULL;
ps->top = ps->capacity = 0;
}
//入栈------栈顶
void StackPush(ST* ps, STDataType x)
{
assert(ps);
if (ps->top == ps->capacity)
{
//增容
int newCapacity = ps->capacity == 0 ? 4 : 2 * ps->capacity;
STDataType* tmp = (STDataType*)realloc(ps->arr, newCapacity * sizeof(STDataType));
if (tmp == NULL)
{
perror("realloc fail!");
exit(1);
}
ps->arr = tmp;
ps->capacity = newCapacity;
}
ps->arr[ps->top++] = x;
}
//栈是否为空
bool StackEmpty(ST* ps)
{
assert(ps);
return ps->top == 0;
}
//出栈------栈顶
void StackPop(ST* ps)
{
assert(!StackEmpty(ps));
ps->top--;
}
//取栈顶元素
STDataType StackTop(ST* ps)
{
assert(!StackEmpty(ps));
return ps->arr[ps->top - 1];
}
//获取栈中有效元素个数
int StackSize(ST* ps)
{
return ps->top;
}
//销毁
void StackDestroy(ST* ps)
{
if (ps->arr)
free(ps->arr);
ps->arr = NULL;
ps->capacity = ps->top = 0;
}
/////////////////////以上是栈的结构和实现///////////////////////
typedef struct
{
ST pushST;
ST popST;
} MyQueue;
MyQueue* myQueueCreate()
{
MyQueue* pq = (MyQueue*)malloc(sizeof(MyQueue));
StackInit(&pq->pushST);
StackInit(&pq->popST);
return pq;
}
void myQueuePush(MyQueue* obj, int x)
{
//往pushST中插入数据
StackPush(&obj->pushST, x);
}
// 检查popST是否为空
// 1)不为空，直接出popST的栈顶
// 2)为空，pushST中的数据导入到popST中，再出popST栈顶
int myQueuePop(MyQueue* obj)
{
if(StackEmpty(&obj->popST))
{
//导数据
while(!StackEmpty(&obj->pushST))
{
int data = StackTop(&obj->pushST);
StackPush(&obj->popST, data);
StackPop(&obj->pushST);
}
}
int top = StackTop(&obj->popST);
StackPop(&obj->popST);
return top;
}
int myQueuePeek(MyQueue* obj)
{
if(StackEmpty(&obj->popST))
{
//导数据
while(!StackEmpty(&obj->pushST))
{
int data = StackTop(&obj->pushST);
StackPush(&obj->popST, data);
StackPop(&obj->pushST);
}
}
int top = StackTop(&obj->popST);
return top;
}
bool myQueueEmpty(MyQueue* obj)
{
return StackEmpty(&obj->pushST) && StackEmpty(&obj->popST);
}
void myQueueFree(MyQueue* obj)
{
StackDestroy(&obj->pushST);
StackDestroy(&obj->popST);
free(obj);
obj = NULL;
}
/**
* Your MyQueue struct will be instantiated and called as such:
* MyQueue* obj = myQueueCreate();
* myQueuePush(obj, x);
* int param_2 = myQueuePop(obj);
* int param_3 = myQueuePeek(obj);
* bool param_4 = myQueueEmpty(obj);
* myQueueFree(obj);
*/