栈的概念
栈是一种特殊的线性表,其只允许在固定的一端进行插入和删除元素操作。进行数据插入和删除操作的一端称为栈顶,另一端称为栈底。栈中的数据元素遵守后进先出LIFO(Last In First Out)的原则。
画个图理解一下
咱们可以观察到,进出数据只在栈顶进行
实现栈用数组最方便
栈的实现
#pragma once
#include<stdio.h>
#include<stdlib.h>
#include<stdbool.h>
#include<assert.h>
typedef int STDataType;typedef struct Stack {STDataType* a;int top;int capacity;
}ST;void STInit(ST* pst);//初始化
void STDestroy(ST* pst);//销毁void STPush(ST* pst, STDataType x);//入栈
void STPop(ST* pst);//出栈STDataType STTop(ST* pst);//获取栈顶元素
int STSize(ST* pst);//获取数据个数bool STEmpty(ST* pst);//判空
#define _CRT_SECURE_NO_WARNINGS 1
#include"Stack.h"
void STInit(ST* pst)
{assert(pst);pst->a = NULL;pst->capacity = 0;pst->top = 0;
}void STDestroy(ST* pst)
{assert(pst);free(pst->a);pst->a = NULL;pst->capacity = 0;pst->top = 0;
}void STPush(ST* pst, STDataType x)
{assert(pst);if (pst->capacity == pst->top) {int newcapacity = pst->capacity == 0 ? 4 : pst->capacity * 2;STDataType* temp = (STDataType*)realloc(pst->a, newcapacity * sizeof(STDataType));//扩容扩的是数组,不是结构体if (temp == NULL) {perror("realloc fail");return;}pst->a = temp;pst->capacity = newcapacity;}pst->a[pst->top] = x;pst->top++;
}
void STPop(ST* pst)
{assert(pst);assert(pst->top > 0);pst->top--;
}STDataType STTop(ST* pst) {assert(pst);return pst->a[pst->top - 1];
}int STSize(ST* pst)
{assert(pst);return pst->top - 1;
}bool STEmpty(ST* pst)
{assert(pst);return pst->top == 0;
}
栈的应用
let's看题目
然后是代码实现
#include<stdio.h>
#include<stdlib.h>
#include<stdbool.h>
#include<assert.h>
typedef char STDataType;typedef struct Stack {STDataType* a;int top;int capacity;
}ST;void STInit(ST* pst)
{assert(pst);pst->a = NULL;pst->capacity = 0;pst->top = 0;
}void STDestroy(ST* pst)
{assert(pst);free(pst->a);pst->a = NULL;pst->capacity = 0;pst->top = 0;
}void STPush(ST* pst, STDataType x)
{assert(pst);if (pst->capacity == pst->top) {int newcapacity = pst->capacity == 0 ? 4 : pst->capacity * 2;ST* temp = (ST*)realloc(pst->a, newcapacity * sizeof(STDataType));//扩容扩的是数组,不是结构体if (temp == NULL) {perror("realloc fail");return;}pst->a = temp;pst->capacity = newcapacity;}pst->a[pst->top] = x;pst->top++;
}
void STPop(ST* pst)
{assert(pst);assert(pst->top > 0);pst->top--;
}STDataType STTop(ST* pst) {assert(pst);return pst->a[pst->top - 1];
}int STSize(ST* pst)
{assert(pst);return pst->top - 1;
}bool STEmpty(ST* pst)
{assert(pst);return pst->top == 0;
}bool isValid(char* s) {ST st;STInit(&st);while(*s){if(*s=='('||*s=='{'||*s=='['){STPush(&st,*s);}else{if(STEmpty(&st)){return false;}char top=STTop(&st);STPop(&st);if((top=='('&&*s!=')')||(top=='{'&&*s!='}')||(top=='['&&*s!=']')){STDestroy(&st);return false;}}++s;}bool ret=STEmpty(&st);STDestroy(&st);return ret;
}