数据结构与算法-栈

　　先进后出的一种数据结构。

　　特殊的数组或者链表，线性表。

　　存在限制条件，只能操作栈顶。

 

一：有趣的题目

1.设计一个括号匹配的功能

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package com.jun.algorithm.foundation.main;   import java.util.Objects;   /**  * 括号问题  * <p>  * 右括号来了，就找栈顶看是否可以匹配，匹配就出栈  * 最后栈应该是空  *  * @author caojun  */ public class Bracket {     public static boolean isOk(String str) {         StackImpl<Character> brackets = new StackImpl<>(20);         char[] chars = str.toCharArray();           for (Character c : chars) {             switch (c) {                 case '{':                 case '(':                 case '[':                     brackets.push(c);                     break;                 case '}':                     if (Objects.equals('{', brackets.pop())) {                         break;                     } else {                         return false;                     }                 case ']':                     if (Objects.equals('[', brackets.pop())) {                         break;                     } else {                         return false;                     }                 case ')':                     if (Objects.equals('(', brackets.pop())) {                         break;                     } else {                         return false;                     }             }         }         return brackets.isEmpty();     } }

　　

　

 

二：栈

1.具体的实现

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package com.jun.algorithm.foundation.main;   /**  * 栈的接口  *  * @param <Item>  * @author caojun  */ public interface IStack<Item> {       void push(Item item);       Item pop();       int size();       boolean isEmpty(); }

　　

　　具体是数组方式实现：

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package com.jun.algorithm.foundation.main;   /**  * 栈的实现  * 通过数组实现  *  * @author caojun  */ public class StackImpl<Item> implements IStack<Item> {       private Item[] a = (Item[]) new Object[1];     private int n = 0;       public StackImpl() {       }       public StackImpl(int cap) {         a = (Item[]) new Object[cap];     }       @Override     public void push(Item item) {         judgeSize();         a[n++] = item;     }       @Override     public Item pop() {         if (isEmpty()) {             return null;         }         Item item = a[--n];         a[n] = null;         return item;     }       @Override     public int size() {         return 0;     }       @Override     public boolean isEmpty() {         return false;     }       private void judgeSize() {         // 扩展         if (a.length < n) {             reSize(2 * a.length);         }         if (n > 0 && n < a.length / 2) {             reSize(a.length / 2);         }     }       private void reSize(int size) {         Item[] temp = (Item[]) new Object[size];         for (int i = 0; i < n; i++) {             temp[i] = a[i];         }         a = temp;     } }