一、用栈实现队列

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

（一）分析题目

（二）编写代码

typedef char STDataType;
typedef struct Stack
{STDataType* a; //int top;	  //相当于数组下标，注意栈为空时，top的值应该为？int capacity;//栈的容量
}ST;void STInit(ST* pst);
void STDestroy(ST* pst);
//入栈
void STPush(ST* pst,STDataType x);
//出栈
void STPop(ST* pst);
//栈顶元素
STDataType STTop(ST* pst);
//判断栈是否为空
bool STEmpty(ST* pst);
//获取size
int STSize(ST* pst);void STInit(ST* pst)
{assert(pst);pst->a = NULL;pst->top = 0;//top指向-1，表示栈顶元素数据   0 栈顶数据下一位置pst->capacity = 0;
}void STDestroy(ST* pst)
{assert(pst);free(pst->a);pst->a = NULL;pst->top = pst->capacity = 0;
}
//判断栈是否为空
bool STEmpty(ST* pst)
{assert(pst);return pst->top == 0;
}
//入栈
void STPush(ST* pst, STDataType x)
{if (pst->top == pst->capacity){int newCapacity = pst->capacity == 0 ? 4 : pst->capacity * 2;STDataType* tmp = realloc(pst->a, newCapacity * sizeof(STDataType));if (tmp == NULL){perror("realloc fail");return;}pst->a = tmp;pst->capacity = newCapacity;}pst->a[pst->top] = x;pst->top++;
}//出栈
void STPop(ST* pst)
{assert(pst);assert(!STEmpty(pst));pst->top--;
}//栈顶元素
STDataType STTop(ST* pst)
{assert(pst);assert(!STEmpty(pst));return pst->a[pst->top - 1];
}//获取size
int STSize(ST* pst)
{assert(pst);return pst->top;
}typedef struct {ST pushst;ST popst;
} MyQueue;MyQueue* myQueueCreate() {MyQueue* obj = (MyQueue*)malloc(sizeof(MyQueue));if(obj ==NULL){perror("malloc fail");return NULL;}STInit(&obj->pushst);STInit(&obj->popst);return obj;
}void myQueuePush(MyQueue* obj, int x) {STPush(&obj->pushst,x);
}int myQueuePeek(MyQueue* obj) {if(STEmpty(&obj->popst)){while(!STEmpty(&obj->pushst)){STPush(&obj->popst,STTop(&obj->pushst));STPop(&obj->pushst);}}return STTop(&obj->popst);
}int myQueuePop(MyQueue* obj) {int front = myQueuePeek(obj);STPop(&obj->popst);return front;
}bool myQueueEmpty(MyQueue* obj) {return STEmpty(&obj->pushst)&&STEmpty(&obj->popst);
}void myQueueFree(MyQueue* obj) {STDestroy(&obj->pushst);STDestroy(&obj->popst);free(obj);
}/*** 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);
*/