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用两个队列实现栈

leetcode

题目描述

思路：

准备两个队列，第一个队列依次出队到只剩一个数据时停止，将已出队的数据依次入队到第二个队列，将第一个队列仅剩的一个数据出队即实现了栈的出栈。入栈时哪个队列不为空则在哪个队列入队。

结构逻辑图如下

完整解析代码

typedef int QDataType;
typedef struct QueueNode
{struct QueueNode* next;QDataType data;
}QNode;typedef struct Queue
{QNode* phead;QNode* ptail;int size;
}Queue;void QueueInit(Queue* pq)
{assert(pq);pq->phead = NULL;pq->ptail = NULL;pq->size = 0;
}
void QueueDestroy(Queue* pq)
{assert(pq);QNode* cur = pq->phead;while (cur) {QNode* next = cur->next;free(cur);cur = next;}pq->phead = pq->ptail = NULL;pq->size = 0;
}
void QueuePush(Queue* pq, QDataType x)
{assert(pq);QNode* newnode = (QNode*)malloc(sizeof(QNode));if (newnode == NULL) {perror("mallloc fail\n");return;}newnode->data = x;newnode->next = NULL;if (pq->ptail == NULL) {assert(pq->phead == NULL);pq->phead = pq->ptail = newnode;}else {pq->ptail->next = newnode;pq->ptail = newnode;}pq->size++;
}
bool QueueEmpty(Queue* pq)
{assert(pq);return pq->size == 0;
}
void QueuePop(Queue* pq)
{assert(pq);assert(!QueueEmpty(pq));if (pq->phead->next == NULL) {free(pq->phead);pq->phead = pq->ptail = NULL;}else {QNode* next = pq->phead->next;free(pq->phead);pq->phead = next;}pq->size--;
}
QDataType QueueFront(Queue* pq)
{assert(pq);assert(!QueueEmpty(pq));return pq->phead->data;
}
QDataType QueueBack(Queue* pq)
{assert(pq);assert(!QueueEmpty(pq));return pq->ptail->data;
}
int QueueSize(Queue* pq)
{assert(pq);return pq->size;
}//------以下为OJ提供-------typedef struct {Queue q1;Queue q2;
} MyStack;MyStack* myStackCreate() {MyStack* obj = (MyStack*)malloc(sizeof(MyStack));if (obj == NULL) {perror("malloc fail");return NULL;}QueueInit(&obj->q1);QueueInit(&obj->q2);return obj;
}void myStackPush(MyStack* obj, int x) {if (!QueueEmpty(&obj->q1)) {QueuePush(&obj->q1, x);}else {QueuePush(&obj->q2, x);}
}int myStackPop(MyStack* obj) {Queue* pEmptyQ = &obj->q1;Queue* pNonEmptyQ = &obj->q2;if (!QueueEmpty(&obj->q1)) {pEmptyQ = &obj->q2;pNonEmptyQ = &obj->q1;}while (QueueSize(pNonEmptyQ) > 1) {QueuePush(pEmptyQ, QueueFront(pNonEmptyQ));QueuePop(pNonEmptyQ);}int top = QueueFront(pNonEmptyQ);QueuePop(pNonEmptyQ);return top;
}int myStackTop(MyStack* obj) {if (!QueueEmpty(&obj->q1)) {return QueueBack(&obj->q1);}else {return QueueBack(&obj->q2);}
}bool myStackEmpty(MyStack* obj) {return QueueEmpty(&obj->q1) &&QueueEmpty(&obj->q2);
}void myStackFree(MyStack* obj) {QueueDestroy(&obj->q1);QueueDestroy(&obj->q2);free(obj);
}