Idea: Find the smallest element before each push into the stack (every time a new element is pushed into the stack, the new element is assumed to be the smallest element min) ( Case 1 : When pushed into the stack, there is no element in the stack, that is, a Empty stack. At this time , push the element to be pushed into the stack first, and then push the smallest element into the stack; * Case 2*: There are already elements in the stack when pushing into the stack, at this time, the minimum value min is compared with the top element of the stack Compare, if the top element of the stack is smaller than the minimum value, assign it to the minimum value min (min is always the minimum value) . Then push the element to be pushed onto the stack and then push the minimum value onto the stack.) As a result, the smallest value is always put on the stack last, so when the top element of the stack is taken, the top element of the stack is always the smallest one .
minStack.h file
#pragma once
typedef char minStackType;
typedef struct minStack
{
minStackType *data;
//有效元素个数
int size;
//表示data段内存中能容纳的元素个数
int capacity;
}minStack;
//初始化函数
void minStackInit(minStack *stack);
//销毁函数
void minStackDestroy(minStack *stack);
//入栈函数
void minStackPush(minStack *stack,minStackType value);
//出栈函数
void minStackPop(minStack *stack);
//取栈顶元素函数
int minStackGetTop(minStack *stack,minStackType *value);minStack.c file
#include<stdio.h>
#include"minSeqStack.h"
#include<stdlib.h>
#define Test_Header printf("\n==========%s==========\n",__FUNCTION__);
//初始化函数
void minStackInit(minStack *stack)
{
if(stack == NULL)
{
//非法输入
return;
}
stack->size = 0;
stack->capacity = 1000;
stack->data = (minStackType*)malloc(stack->capacity * sizeof(minStackType));
}
//销毁函数
void minStackDestroy(minStack *stack)
{
if(stack == NULL)
{
//非法输入
return;
}
free(stack->data);
stack->data = NULL;
stack->size = 0;
stack->capacity = 0;
}
//入栈函数
void minStackPush(minStack *stack,minStackType value)
{
if(stack == NULL)
{
//非法输入
return;
}
//每一次入栈前判断栈是否满了
if(stack->size == stack->capacity)
{
//栈满了，没有空间可供新元素插入
return;
}
//假定要插入的值就是最小的值
minStackType min = value;
if(stack->size == 0)
{
//空栈
//每次入栈两次，最小的值总是最后入栈
stack->data[stack->size++] = value;
stack->data[stack->size++] = min;
}
//不是空栈
else
{
//如果当前栈中的栈顶元素比假定的最小值还要小
if(min > stack->data[stack->size-1])
{
//改变最小值
min = stack->data[stack->size-1];
}
//先将value入栈，再将最小值入栈
stack->data[stack->size++] = value;
stack->data[stack->size++] = min;
}
}
//出栈函数
void minStackPop(minStack *stack)
{
if(stack == NULL)
{
//非法输入
return;
}
if(stack->size == 0)
{
//空栈，没有元素可以出栈
return;
}
//不是空栈
else
{
//此时需要出栈两个元素才会将我们最后插入的元素（包括一个新的值和最后插入的最小的值）出栈
stack->size -= 2;
}
}
//取栈顶元素函数，成功取到栈顶元素就返回1，否则返回0
int minStackGetTop(minStack *stack,minStackType *value)
{
if(stack == NULL)
{
//非法输入
return 0;
}
if(stack->size == 0)
{
//空栈
return 0;
}
//不是空栈
*value = stack->data[stack->size-1];
return 1;
}
void Print(minStack *stack,const char *msg)
{
printf("[%s]\n",msg);
if(stack == NULL)
{
//非法输入
return;
}
if(stack->size == 0)
{
//空栈
return;
}
int i = 0;
for(;i < stack->size;i++)
{
printf("%c ",stack->data[i]);
}
printf("\n");
}
void TestMinSeqStack()
{
Test_Header;
minStack stack;
//初始化栈并测试
minStackInit(&stack);
printf("expected size = 0,capacity = 1000,actual size = %d,capacity = %d\n\n",stack.size,stack.capacity);
//入栈函数测试
minStackPush(&stack,'x');
minStackPush(&stack,'y');
Print(&stack,"入栈2个元素：x y");
//以下为取栈顶元素函数测试（栈顶元素总是最小值）
minStackType value;
int ret = minStackGetTop(&stack,&value);
printf("expected ret = 1,actual ret = %d\n",ret);
printf("expected min = x,actual min = %c\n\n",value);
minStackPush(&stack,'g');
Print(&stack,"再入栈一个元素:g");
ret = minStackGetTop(&stack,&value);
printf("expected ret = 1,actual ret = %d\n",ret);
printf("expected min = g,actual min = %c\n\n",value);
minStackPush(&stack,'w');
Print(&stack,"再入栈一个元素:w");
ret = minStackGetTop(&stack,&value);
printf("expected ret = 1,actual ret = %d\n",ret);
printf("expected min = g,actual min = %c\n\n",value);
//出栈函数测试
minStackPop(&stack);
minStackPop(&stack);
minStackPop(&stack);
minStackPop(&stack);
Print(&stack,"将所有元素出栈");
//空栈取栈顶元素测试
ret = minStackGetTop(&stack,&value);
printf("expected ret = 0,actual ret = %d\n\n",ret);
//销毁栈
minStackDestroy(&stack);
printf("expected size = 0,capacity = 0,actual size = %d,capacity = %d\n\n",stack.size,stack.capacity);
}
//主函数调用测试函数
int main()
{
TestMinSeqStack();
return 0;
}The test results are as follows:
