Stack经典问题—最小栈retrieving the minimum element in constant time

最小栈解决O(1)时间复杂度内最小值的查找

题目描述
Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
要求在常数时间内找到栈中最小值为重点要求。即时间复杂度为O(1)。
题目作者：力扣 (LeetCode)
链接：https://leetcode-cn.com/leetb...
题目来源：力扣（LeetCode）
题解作者：WildDuck
题目分析

代码实现

#define Elemtype int
struct MinStack
{
    Elemtype val;
    struct MinStack* next;
    struct MinStack* Min_stack;
};

typedef struct MinStack MinStack;
typedef struct MinStack* MinStack_pointer;

/** initialize your data structure here. */

//使用链式存储结构实现栈 严格限制从头部开始操作
MinStack* minStackCreate() 
{
    //头部指针作为栈顶位置，标识并控制整个栈
    MinStack_pointer head = (MinStack_pointer)malloc(sizeof(struct MinStack));
    head->val = -1;
    head->next = NULL;
    head->Min_stack = NULL;
    return head;
}

void minStackPush(MinStack* obj, int val) 
{
    //根据链式结构实现栈，栈的push必须用头插法实现
    //此类实现方式的好处高效使用内存空间、不限定栈大小情况下不会溢出
    MinStack_pointer new_elem = (MinStack_pointer)malloc(sizeof(struct MinStack));
    obj -> val = obj -> val + 1;
    new_elem -> val = val;
    new_elem -> next = obj -> next;
    new_elem -> Min_stack = NULL;
    obj ->next = new_elem;
    
    if(obj -> Min_stack == NULL)
    {
        obj -> Min_stack = new_elem;
    }
    else if(obj -> Min_stack != NULL && (obj -> Min_stack -> val) > val)
    {
        obj -> Min_stack = new_elem;
    }
    new_elem -> Min_stack = obj->Min_stack;
}

void minStackPop(MinStack* obj) 
{
    //根据链式结构实现栈，栈的push必须用头删法实现
    MinStack_pointer temp_elem = obj->next;
    if(obj->Min_stack == obj->next)
    {
        if(obj->val > 0)
        {
            obj -> Min_stack = ((obj->next)->next)->Min_stack;
        }
        else if(obj->val == 0)
        {
            obj -> Min_stack = NULL;
        }
        
    }
    obj -> next = obj->next->next;
    obj -> val = obj -> val -1;
    free(temp_elem);
}

int minStackTop(MinStack* obj) 
{
    return obj->next->val;
}

int minStackGetMin(MinStack* obj) 
{
    
    return obj->Min_stack->val;
}

/**
 * Your MinStack struct will be instantiated and called as such:
 * MinStack* obj = minStackCreate();
 * minStackPush(obj, val);
 
 * minStackPop(obj);
 
 * int param_3 = minStackTop(obj);
 
 * int param_4 = minStackGetMin(obj);
*/