08-栈

第一种方式：继承（ArrayList）
这种方式会存在问题：Array 里面所有的方法都可以访问，但有些方法对栈不适用

package com.weyan;

import com.weyan.list.ArrayList;

public class Stack<E> extends ArrayList<E> {
    public void clear() {
        list.clear();
    }
    public void push(E element) {
        add(element);
    }
    
    public E pop() {
        return remove(size - 1);
    }
    
    public E top() {
        return get(size - 1);
    }
    
}

验证结果：

---

第二种方式：ArrayList 作为为栈的一部分

import com.weyan.list.ArrayList;

public class Stack<E> {
    private ArrayList<E> list = new ArrayList<>();
    
    public void push(E element) {
        list.add(element);
    }
    
    public E pop() {
        return list.remove(list.size() - 1);
    }
    
    public E top() {
        return list.get(list.size() - 1);
    }
    
    public boolean isEmpty() {
        return list.isEmpty();
    }
    
}

---

代码一：

package 栈;

import java.util.HashMap;
import java.util.Stack;

import org.omg.CORBA.PUBLIC_MEMBER;

public class _20_有效的括号 {
    /** _20_有效的括号
     * url:https://leetcode-cn.com/problems/valid-parentheses/solution/
     */
    public Boolean isValid1(String s) {
        Stack<Character> stack = new Stack<Character>();
        int len = s.length();
        for (int i = 0; i < len; i++) {
            char c = s.charAt(i);
            if (c == '(' || c == '[' || c == '{') {
                stack.push(c);
            }else {
                if (stack.isEmpty()) return false;
                char left = stack.pop();
                if (left == '(' && c != ')') return false;
                if (left == '[' && c != ']') return false;
                if (left == '{' && c != '}') return false;
            }
        }
        return stack.isEmpty();
    }
    
    /** _20_有效的括号
     * url:https://leetcode-cn.com/problems/valid-parentheses/solution/
     */
//  private sta HashMap<Character, Character> map = new HashMap<Character, Character>();
//  public _20_有效的括号() { 
//      //key - value
//      map.put('(', ')');
//      map.put('[', ']');
//      map.put('{', '}');
//  }
    private static HashMap<Character, Character> map = new HashMap<Character, Character>();
    static { 
        //key - value
        map.put('(', ')');
        map.put('[', ']');
        map.put('{', '}');
    }
    public Boolean isValid2(String s) {
        Stack<Character> stack = new Stack<Character>();
        int len = s.length();
        for (int i = 0; i < len; i++) {
            char c = s.charAt(i);
            if (map.containsKey(c)) {
                stack.push(c);
            }else {
                if (stack.isEmpty()) return false;
                char left = stack.pop();
                if (c != map.get(left)) return false;
            }
        }
        return stack.isEmpty();
    }
    
}