[LeetCode-232] Implement Queue using Stacks（两个栈实现一个队列）

Implement the following operations of a queue using stacks.

• push(x) -- Push element x to the back of queue.
• pop() -- Removes the element from in front of queue.
• peek() -- Get the front element.
• empty() -- Return whether the queue is empty.

Notes:

• You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid.
• Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
• You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

实现一

思路

    s1是入栈的，s2是出栈的。

• 入队列，直接压到s1是就行了
• 出队列，先把s1中的元素全部出栈压入到s2中，弹出s2中的栈顶元素；再把s2的所有元素全部压回s1中

实现二

思路

    s1是入栈的，s2是出栈的。保证所有元素都在一个栈里面

• 入队列时：如果s1为空，把s2中所有的元素倒出压到s1中；否则直接压入s1
• 出队列时：如果s2不为空，把s2中的栈顶元素直接弹出；否则，把s1的所有元素全部弹出压入s2中，再弹出s2的栈顶元素

比较：与实现一相比较，出队列时不必每次都捣鼓了。

实现三

思路

    s1是入栈的，s2是出栈的。

• 入队列：直接压入s1即可
• 出队列：如果s2不为空，把s2中的栈顶元素直接弹出；否则，把s1的所有元素全部弹出压入s2中，再弹出s2的栈顶元素

比较

    与实现二相比较，入队直接入即可，感觉此时已是最优。

代码实现如下：

// LeetCode232-Implement Queue using Stacks.cpp : 定义控制台应用程序的入口点。////两个栈模拟一个队列//Written by ZP1015//2015.10.21#include "stdafx.h"#include <stdlib.h>#include <stdio.h>#include <string.h>struct STACK_NODE{    int* pData;/*数组，长度为StackLenMax*/    int top;//栈顶指针的位置    int StackLenMax;};typedef struct {struct STACK_NODE *pStackNode_First;struct STACK_NODE* pStackNode_Second;} Queue;struct STACK_NODE* alloc_stack(int StackSize){        if(StackSize <= 0)        return NULL;struct STACK_NODE* pStackNode = NULL;    pStackNode = (struct STACK_NODE*)malloc(sizeof(struct STACK_NODE));    if(NULL == pStackNode) {return NULL;    }    memset(pStackNode, 0, sizeof(struct STACK_NODE));    pStackNode->pData = (int *)malloc(sizeof(int)*StackSize);    if(NULL == pStackNode->pData){goto malloc_failed;    }    memset(pStackNode->pData, 0, sizeof(int) * StackSize);    pStackNode->top= -1; /*初始化从0开始*/pStackNode->StackLenMax = StackSize;    return pStackNode;malloc_failed:free(pStackNode);return NULL;}int free_stack(struct STACK_NODE* pStackNode){    if(NULL == pStackNode)        return -1;    if(NULL == pStackNode->pData) {free(pStackNode);return -1;}    free(pStackNode->pData);    free(pStackNode);    return 0;}int stack_push(struct STACK_NODE* pStackNode, int value){/*1.异常处理*/    if(NULL == pStackNode)        return -1;if(NULL == pStackNode->pData) {return -1;}/*2.栈满，不能压入元素*/    if(pStackNode->top == pStackNode->StackLenMax-1)        return -1;++pStackNode->top;    pStackNode->pData[pStackNode->top] = value;    return 0;}int stack_pop(struct STACK_NODE* pStackNode, int* value){    if(NULL == pStackNode || NULL == value)        return -1;    if(-1 == pStackNode->top)        return -1;    *value = pStackNode->pData[pStackNode->top];pStackNode->top--;    return 0;}int count_stack_number(struct STACK_NODE* pStackNode){    return (pStackNode->top+1);}void print_stack_node(struct STACK_NODE *pStackNode) {/*1.输入的参数有误*/    if(NULL == pStackNode) {printf("[%d] pStackNode is illegal! \n",__LINE__);return;    }/*2.输入的链式堆栈为空*/if(-1 == pStackNode->top) {printf("[%d] pStackNode is empty!\n",__LINE__);return ;}struct STACK_NODE *pStackNodeTemp = pStackNode;int count = 0;while(count <= pStackNode->top) {printf("%d ",pStackNodeTemp->pData[count]);count++;;}printf("\n");}/* Create a queue */void queueCreate(Queue *queue, int maxSize) {if(!queue) {return;}if(maxSize<=0)return;/*创建两个栈*/    queue->pStackNode_First = alloc_stack(maxSize);queue->pStackNode_Second = alloc_stack(maxSize);}/* Push element x to the back of queue */void queuePush(Queue *queue, int element) {if(!queue) return;/*1.栈1入队列，实现入栈功能*/    stack_push(queue->pStackNode_First,element);}/* Removes the element from front of queue */void queuePop(Queue *queue) {/*1.链表2为空*/int a = 0;    if(queue->pStackNode_Second->top == -1) {while(queue->pStackNode_First->top != -1) {stack_pop(queue->pStackNode_First,&a);stack_push(queue->pStackNode_Second,a);}}if(queue->pStackNode_Second->top == -1)return;/*栈2弹栈，实现出队列功能*/stack_pop(queue->pStackNode_Second,&a);}/* Get the front element */int queuePeek(Queue *queue) {if(!queue) return -1;    /*1.链表2为空*/int a = 0;    if(queue->pStackNode_Second->top == -1) {while(queue->pStackNode_First->top != -1) {stack_pop(queue->pStackNode_First,&a);stack_push(queue->pStackNode_Second,a);}}if(queue->pStackNode_Second->top == -1)return -1;/*栈2弹栈，实现出队列功能*/return (queue->pStackNode_Second->pData[queue->pStackNode_Second->top]);}    /* Return whether the queue is empty */bool queueEmpty(Queue *queue) {if(!queue) return 1;if(queue->pStackNode_Second->top == -1&&queue->pStackNode_First->top == -1)return 1;return 0;}/* Destroy the queue */void queueDestroy(Queue *queue) {if(!queue) return;free_stack(queue->pStackNode_First);free_stack(queue->pStackNode_Second); }void print_queue_node(Queue *queue) {/*1.输入的参数有误*/    if(!queue) return;print_stack_node(queue->pStackNode_First);print_stack_node(queue->pStackNode_Second);}

全部代码实现：

// LeetCode232-Implement Queue using Stacks.cpp : 定义控制台应用程序的入口点。////两个栈模拟一个队列//Written by ZP1015//2015.10.21#include "stdafx.h"#include <stdlib.h>#include <stdio.h>#include <string.h>struct STACK_NODE{    int* pData;/*数组，长度为StackLenMax*/    int top;//栈顶指针的位置    int StackLenMax;};typedef struct {struct STACK_NODE *pStackNode_First;struct STACK_NODE* pStackNode_Second;} Queue;struct STACK_NODE* alloc_stack(int StackSize){        if(StackSize <= 0)        return NULL;struct STACK_NODE* pStackNode = NULL;    pStackNode = (struct STACK_NODE*)malloc(sizeof(struct STACK_NODE));    if(NULL == pStackNode) {return NULL;    }    memset(pStackNode, 0, sizeof(struct STACK_NODE));    pStackNode->pData = (int *)malloc(sizeof(int)*StackSize);    if(NULL == pStackNode->pData){goto malloc_failed;    }    memset(pStackNode->pData, 0, sizeof(int) * StackSize);    pStackNode->top= -1; /*初始化从0开始*/pStackNode->StackLenMax = StackSize;    return pStackNode;malloc_failed:free(pStackNode);return NULL;}int free_stack(struct STACK_NODE* pStackNode){    if(NULL == pStackNode)        return -1;    if(NULL == pStackNode->pData) {    free(pStackNode);return -1;}    free(pStackNode->pData);    free(pStackNode);    return 0;}int stack_push(struct STACK_NODE* pStackNode, int value){/*1.异常处理*/    if(NULL == pStackNode)        return -1;if(NULL == pStackNode->pData) {return -1;}/*2.栈满，不能压入元素*/    if(pStackNode->top == pStackNode->StackLenMax-1)        return -1;++pStackNode->top;    pStackNode->pData[pStackNode->top] = value;    return 0;}int stack_pop(struct STACK_NODE* pStackNode, int* value){    if(NULL == pStackNode || NULL == value)        return -1;    if(-1 == pStackNode->top)        return -1;    *value = pStackNode->pData[pStackNode->top];pStackNode->top--;    return 0;}int count_stack_number(struct STACK_NODE* pStackNode){    return (pStackNode->top+1);}void print_stack_node(struct STACK_NODE *pStackNode) {/*1.输入的参数有误*/    if(NULL == pStackNode) {printf("[%d] pStackNode is illegal! \n",__LINE__);return;    }/*2.输入的链式堆栈为空*/if(-1 == pStackNode->top) {printf("[%d] pStackNode is empty!\n",__LINE__);return ;}struct STACK_NODE *pStackNodeTemp = pStackNode;int count = 0;while(count <= pStackNode->top) {printf("%d ",pStackNodeTemp->pData[count]);count++;;}printf("\n");}/* Create a queue */void queueCreate(Queue *queue, int maxSize) {if(!queue) {return;}if(maxSize<=0)return;/*创建两个栈*/    queue->pStackNode_First = alloc_stack(maxSize);queue->pStackNode_Second = alloc_stack(maxSize);}/* Push element x to the back of queue */void queuePush(Queue *queue, int element) {if(!queue) return;/*1.栈1入队列，实现入栈功能*/    stack_push(queue->pStackNode_First,element);}/* Removes the element from front of queue */void queuePop(Queue *queue) {/*1.链表2为空*/int a = 0;    if(queue->pStackNode_Second->top == -1) {while(queue->pStackNode_First->top != -1) {stack_pop(queue->pStackNode_First,&a);stack_push(queue->pStackNode_Second,a);}}if(queue->pStackNode_Second->top == -1)return;/*栈2弹栈，实现出队列功能*/stack_pop(queue->pStackNode_Second,&a);}/* Get the front element */int queuePeek(Queue *queue) {if(!queue) return -1;    /*1.链表2为空*/int a = 0;    if(queue->pStackNode_Second->top == -1) {while(queue->pStackNode_First->top != -1) {stack_pop(queue->pStackNode_First,&a);stack_push(queue->pStackNode_Second,a);}}if(queue->pStackNode_Second->top == -1)return -1;/*栈2弹栈，实现出队列功能*/return (queue->pStackNode_Second->pData[queue->pStackNode_Second->top]);}    /* Return whether the queue is empty */bool queueEmpty(Queue *queue) {if(!queue) return 1;if(queue->pStackNode_Second->top == -1&&queue->pStackNode_First->top == -1)return 1;return 0;}/* Destroy the queue */void queueDestroy(Queue *queue) {if(!queue) return;free_stack(queue->pStackNode_First);free_stack(queue->pStackNode_Second); }void print_queue_node(Queue *queue) {/*1.输入的参数有误*/    if(!queue) return;print_stack_node(queue->pStackNode_First);print_stack_node(queue->pStackNode_Second);}int main(){Queue pStackNode;queueCreate(&pStackNode,20);int i = 0;for (i = 0;i<10;i++) {queuePush(&pStackNode,i);/*入栈*/}print_queue_node(&pStackNode);/*出栈*/queuePop(&pStackNode);print_queue_node(&pStackNode);/*获得栈顶元素*/printf("top %d\n",queuePeek(&pStackNode));queueDestroy(&pStackNode);getchar();getchar();return 0;}