算法刷题 DAY10

LeetCode：232.用栈实现队列

//两个栈，负负得正→先进先出
//题目都是合法操作，不用判断操作是否合法（如对空栈进行弹栈）
typedef struct {
    int stack_in[100];
    int stack_out[100];
    int stack_in_top;
    int stack_out_top;
} MyQueue;

MyQueue* myQueueCreate() {
    MyQueue* p = (MyQueue*)malloc(sizeof(MyQueue));
    p->stack_in_top = 0;//莫忘初始化top
    p->stack_out_top = 0;
    return p;
}

void myQueuePush(MyQueue* obj, int x) {
    obj->stack_in[(obj->stack_in_top)++] = x;
}

int myQueuePop(MyQueue* obj) {
    //出栈有元素→直接出队；出栈为空→先把入栈元素全部放到出栈再出队
    if (obj->stack_out_top == 0) {
        while (obj->stack_in_top != 0)
            obj->stack_out[(obj->stack_out_top)++] =//入栈后++
                obj->stack_in[--(obj->stack_in_top)];//弹栈先--
    }

    obj->stack_out_top -= 1;//逻辑出栈
    return obj->stack_out[obj->stack_out_top];
}

int myQueuePeek(MyQueue* obj) {
    int x = myQueuePop(obj);//复用pop函数，类似功能优先进行复用
    obj->stack_out_top += 1;//恢复栈帧
    return x;
}

bool myQueueEmpty(MyQueue* obj) {
    return obj->stack_in_top == 0 && obj->stack_out_top == 0;
}

void myQueueFree(MyQueue* obj) {
    obj->stack_in_top = 0;
    obj->stack_out_top = 0;
}

/**
 * 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);
*/

225. 用队列实现栈

//链表头插法实现

typedef struct list_node{
    int val;
    struct list_node *next;//命名还未完成，要加struct
}list_node;

typedef struct {
    list_node* top;//栈顶
} MyStack;


MyStack* myStackCreate() {
    MyStack *obj=(MyStack*)calloc(1,sizeof(MyStack));
    return obj;
}

void myStackPush(MyStack* obj, int x) {
    list_node* p=(list_node*)calloc(1,sizeof(list_node));
    p->val=x;
    p->next=obj->top;//头插法
    obj->top=p;
}

int myStackPop(MyStack* obj) {
    list_node* temp=obj->top;
    obj->top=obj->top->next;
    int x=temp->val;
    free(temp);
    return x;
}

int myStackTop(MyStack* obj) {
    return obj->top->val;
}

bool myStackEmpty(MyStack* obj) {
    return obj->top==NULL;
}

void myStackFree(MyStack* obj) {
    if(obj->top==NULL) return;
    list_node* p=obj->top;
    while(obj->top){
        obj->top=obj->top->next;
        free(p);//要free p不能直接free top 不然会出现double free 问题
        p=obj->top;
    }
}

/**
 * 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);
*/