栈

概念以及代码实现

栈是仅限于在表尾进行插入和删除的线性表,它遵循先进后出,后进先出原则

• 所以可以在递归,判断回文,反转链表…

代码实现部分java

public interface Stack_i <T>{//入栈void push(T e);//出栈T pop();//获取栈顶元素T peek();//获取栈的元素个数int size();//栈是否为空boolean isEmpty();
}

import java.util.Random;
public class MyArr<T> {private int capacity = 0;private int size = 0;private T[] arr;public MyArr(int capacity) {if (capacity < 0) this.capacity = 10; //if no right input, we will initial capacity 10this.capacity = capacity;this.arr = (T[]) new Object[capacity];}public int getCapacity() {return capacity;}public int getSize() {return size;}public T[] setCapacity(int capacity) {if (capacity < 0) {throw new RuntimeException("扩大小异常");}this.capacity = capacity;T[] newNum = (T[]) new Object[capacity];for (int i = 0; i < this.size; ++i) {newNum[i] = this.arr[i];}return newNum;}//增加元素public void add(T val) {if (this.size >= this.capacity) {this.arr = setCapacity(2 * this.capacity);}this.arr[this.size++] = val;}//数组末尾增加元素public void addLst(T val){this.add(val);}//删除元素public  T removeByIndex(int index) {if (index < 0 || index > this.capacity) {throw new RuntimeException("数组越界");}for (int i = index; i < size - 1; ++i) {arr[i] = arr[i + 1];}size--;if (size < this.capacity / 4 && this.capacity > 4) {arr = setCapacity(this.capacity / 4);}return this.arr[index];}//删除数组末尾元素public T removeLast(){return this.removeByIndex(this.size-1);}//修改位置元素public void modify(int index, T val) {if (index < 0 || index > size - 1) {throw new RuntimeException("数组越界");}arr[index] = val;}//获取某元素位置public int locateVal(T val) {for (int i = 0; i < size; ++i) {if (arr[i] == val) {return i;//return index}}// if no find return -1return -1;}//获取尾元素public T getLast(){return this.arr[this.size-1];}//打印元素@Overridepublic String toString() {StringBuffer stringBuffer = new StringBuffer();stringBuffer.append('[');for (int i = 0; i < this.size - 1; ++i) {stringBuffer.append(arr[i] + ",");}if(size>0) stringBuffer.append(arr[size - 1]);stringBuffer.append(']');return stringBuffer.toString();}}

public class StackImplement<T> implements Stack_i<T>{private MyArr<T> data;private int size=0;@Overridepublic void push(T e) {this.size++;this.data.addLst(e);}public StackImplement() {data = new MyArr<>(10);}@Overridepublic T pop() {if(this.isEmpty()){throw new RuntimeException("栈为空");}return this.data.removeLast();}@Overridepublic T peek() {return this.data.getLast();}@Overridepublic int size() {return this.size;}@Overridepublic boolean isEmpty() {if(size==0)return true;return false;}public int getCapacity(){return this.data.getCapacity();}
}

c语言实现(顺序栈)

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <stdlib.h>
#define OK 1
#define ERROR 0
#define OVERFLOW 0
#define MAXSIZE 10
typedef int Status;
typedef int Element;//声明栈的顺序结构定义
typedef struct {Element* base;Element* top;int stackSize;
}SqStack;
//栈的功能
Status InitStack(SqStack* S);//初始化栈
Status Push(SqStack* S, Element e);//入栈操作
Status Pop(SqStack* S, Element* e);//出栈操作,并返回出去的值
Status IsEmpty(SqStack S);//判断栈是否为空
void PrintStack(SqStack S);//打印栈
Status OperateMenu();//用户界面选择
Element GetTop(SqStack S);//获取头元素
void DestroyStack(SqStack* S);//销毁链表
Status ClearStack(SqStack* S);//清理栈中元素
int StackLen(SqStack S);//获取栈长度int main() {SqStack S;/*赋值为NULL，确保变量具有一个初始状态，避免出现潜在问题,如果没有初始化，系统会分配一个随机地址，在后面对指针修改访问时可能会程序崩溃*/S.base = NULL;S.top = NULL;S.stackSize = 0;int choice;//记录用户选择Element e;//元素类型int temp = 0;//接受函数返回值int len;//获取栈长度while (OK) {choice = OperateMenu();switch (choice){case 1:InitStack(&S);printf("初始化栈\n");break;case 2:printf("请输入要入栈的元素\n");scanf("%d", &e);temp = Push(&S, e);if(temp==-1){printf("此栈未被初始化！\n");break;}printf("入栈成功!\n");PrintStack(S);//打印元素break;case 3:temp = Pop(&S, &e);if(temp==-1){printf("此栈未被初始化！\n");break;}if (temp == ERROR) {printf("栈空!\n");break;}printf("出栈的元素为:%d\n", e);PrintStack(S);break;case 4:temp = IsEmpty(S);if(temp==-1){printf("此栈未被初始化！\n");break;}if (temp == ERROR) {printf("不为空栈!\n");PrintStack(S);break;}printf("为空栈\n");break;case 5:PrintStack(S);break;case 6:e = GetTop(S);if(e==-2){printf("此栈未被初始化！\n");break;}if (e == -1) {printf("为空栈\n");break;}printf("栈顶元素为: %d\n", e);PrintStack(S);break;case 7:temp = ClearStack(&S);if(temp==-1){printf("此栈未被初始化！\n");break;}printf("清理成功!\n");break;case 8:len = StackLen(S);if(len == -1){printf("此栈未被初始化！\n");break;}printf("链表长度为:%d\n", len);PrintStack(S);break;case 9:DestroyStack(&S);printf("销毁成功\n");break;default:exit(OVERFLOW);}}return 0;
}
Status InitStack(SqStack* S) {S->base = (Element*)malloc(sizeof(Element) * MAXSIZE);if (S->base == NULL) {exit(OVERFLOW);//申请失败,异常结束程序}S->top = S->base;S->stackSize = MAXSIZE;//申请成功return OK;
}
Status Push(SqStack* S,Element e) {//判断栈是否初始化if(S->top==NULL||S->base==NULL){printf("此栈未被初始化！\n");return -1;}//判断栈是否满if (S->top - S->base == S->stackSize) {S->base = (Element*)realloc(S->base, sizeof(Element) * MAXSIZE);S->stackSize += MAXSIZE;S->top = S->base + MAXSIZE;}*(S->top) = e;S->top++;//插入完毕return OK;
}
Status Pop(SqStack* S, Element* e) {if(S->top==NULL||S->base==NULL)return -1;//此栈未被初始化if (S->top == S->base)return ERROR;//此时为空栈*e = *(--S->top);//出栈成功return OK;
}
Status IsEmpty(SqStack S) {if(S.top==NULL||S.base==NULL)return -1;//此栈未被初始化if (S.base == S.top)return OK;//判断空栈else return ERROR;
}
void PrintStack(SqStack S) {if(S.top==NULL||S.base==NULL){printf("此栈未被初始化\n");return;//此栈未被初始化}if (S.base == S.top) {printf("此栈为空栈\n");return;}Element* ptr = --S.top;while (ptr!=S.base) {printf("%d\t", *ptr);--ptr;}//打印栈底元素printf("%d", *S.base);printf("\n");return;
}
Status OperateMenu() {int choice = 0;//记录用户选择printf("----------------欢迎使用栈----------------\n");printf("----------------1.初始化栈----------------\n");printf("----------------2.入栈操作----------------\n");printf("----------------3.出栈操作----------------\n");printf("----------------4.判断栈是否为空----------\n");printf("----------------5.打印栈------------------\n");printf("----------------6.获取头元素--------------\n");printf("----------------7.清空列表元素------------\n");printf("----------------8.获取栈的长度------------\n");printf("----------------9.销毁栈------------------\n");printf("----------------10.退出--------------------\n");printf("----------------请输入选项----------------\n");scanf("%d", &choice);return choice;}
Element GetTop(SqStack S) {if(S.top==NULL||S.base==NULL)return -2;//此栈未被初始化if (S.base == S.top) return -1;	return *(--S.top);
}
void DestroyStack(SqStack* S) {S->base = NULL;S->top = NULL;S->stackSize = 0;
}
Status ClearStack(SqStack* S) {if(S->top==NULL||S->base==NULL)return -1;//此栈未被初始化if (S->top == S->base)return ERROR;//空表S->top = S->base;return OK;
}
int StackLen(SqStack S) {if(S.top==NULL||S.base==NULL)return -1;//此栈未被初始化return S.top - S.base;
}

例题

232. 用栈实现队列

1614. 括号的最大嵌套深度

javaclass Solution {public int maxDepth(String s) {// 使用top表示栈顶指针int top = 0;// 记录括号数量int res = 0;for (int i = 0; i < s.length(); ++i) {// 如果碰见左括号说明 括号深度增加 即入栈if (s.charAt(i) == '(') {++top;// 记录最大深度if (top > res) {res = top;}// 碰到右括号出栈 深度就减少} else if (s.charAt(i) == ')') {--top;}}return res;}
}

234. 回文链表

输入：head = [1,2,2,1]
输出：true

输入：head = [1,2]
输出：false

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public boolean isPalindrome(ListNode head) {// 利用栈的先进后出原则 /*可以把链表节点都入栈 然后逐一出栈 栈底指针与栈顶指针对比元素即可*/int[] stack = new int[100001];int base = 0;int top = 0;ListNode p = head;while (p != null) {stack[top++] = p.val;p = p.next;}--top;while(base<=top){if(stack[base]!=stack[top])return false;base = base+1;top = top-1;}return true;}
}

1614. 括号的最大嵌套深度

LCR 123. 图书整理 I

206. 反转链表

402. 移掉 K 位数字

844. 比较含退格的字符串

LCR 036. 逆波兰表达式求值

[面试题 03.01. 三合一](