算法训练——剑指offer(队列 & 栈)摘要

摘要

一、队列 & 栈原理与解题方法

二、队列 & 栈相关算法练习题目

2.1 两个栈实现队列

用两个栈实现队列_牛客题霸_牛客网

package 栈和队列;

import java.util.Stack;

/**
 * @Classname JZ9用两个栈实现队列
 * @Description TODO
 * @Date 2022/2/1 18:22
 * @Created by xjl
 */
public class JZ9用两个栈实现队列 {
    Stack<Integer> stack1 = new Stack<Integer>();
    Stack<Integer> stack2 = new Stack<Integer>();

    public void push(int node) {
        while (!stack2.isEmpty()){
            stack1.add(stack2.pop());
        }
        stack1.add(node);
    }

    public int pop() {
        while (!stack1.isEmpty()){
            stack2.add(stack1.pop());
        }
        return stack2.pop();
    }

    public void push1(int node) {
        stack1.push(node);
    }

    public int pop1() {
        if(stack1.empty()&&stack2.empty()){
            throw new RuntimeException("Queue is empty!");
        }
        if(stack2.empty()){
            while(!stack1.empty()){
                stack2.push(stack1.pop());
            }
        }
        return stack2.pop();
    }
}

2.2 包含最小的min的栈

包含min函数的栈_牛客题霸_牛客网

package 栈和队列;

import java.util.Stack;

/**
 * @Classname JZ30包含min函数的栈
 * @Description TODO
 * @Date 2022/2/1 18:47
 * @Created by xjl
 */
public class JZ30包含min函数的栈 {

    Stack<Integer> stack = new Stack<Integer>();

    public void push(int node) {
        if (stack.isEmpty()) {
            stack.add(node);
            stack.add(node);
        } else {
            int value=stack.peek();
            if (value>=node){
                stack.add(node);
                stack.add(node);
            }else {
                stack.add(node);
                stack.add(value);
            }
        }
    }

    public void pop() {
        stack.pop();
        stack.pop();
    }

    public int top() {
        int n1=stack.pop();
        int n2=stack.pop();
        stack.add(n2);
        stack.add(n1);
        return n2;
    }

    public int min() {
        int tmp=stack.peek();
        return tmp;
    }

    Stack<Integer> stack1 = new Stack<Integer>();
    Stack<Integer> stack2 = new Stack<Integer>();

    public void push1(int node) {
        stack1.add(node);
        if (stack2.isEmpty()){
            stack2.add(node);
        }else {
            if (node<stack2.peek()){
                stack2.add(node);
            }else {
                stack2.add(stack2.peek());
            }
        }
    }

    public void pop1() {
        stack1.pop();
        stack2.pop();
    }

    public int top1() {
        return stack1.peek();
    }

    public int min1() {
        return stack2.peek();
    }


    public static void main(String[] args) {
        JZ30包含min函数的栈 j=new JZ30包含min函数的栈();
        j.push(1);
        j.push(0);
        j.push(-3);
        j.min();
        j.pop();
        j.top();
        j.min();
    }

}

2.3 栈的压入和弹出序列

栈的压入、弹出序列_牛客题霸_牛客网

package 栈和队列;

import java.util.Stack;

/**
 * @Classname JZ31栈的压入弹出序列
 * @Description TODO
 * @Date 2022/2/2 9:07
 * @Created by xjl
 */
public class JZ31栈的压入弹出序列 {

    public boolean IsPopOrder(int[] pushA, int[] popA) {
        Stack<Integer> stack = new Stack();
        int pushIndex = 0, popIndex = 0;

        while(pushIndex < pushA.length){
            //入栈
            stack.push(pushA[pushIndex++]);
            //判断出栈的后的是否一致
            while(popIndex<popA.length && !stack.isEmpty() && stack.peek()==popA[popIndex]){
                stack.pop();
                popIndex++;
            }
        }
        //判断是全部出栈了
        return stack.isEmpty();
    }
}

2.4 翻转单词序列

翻转单词序列_牛客题霸_牛客网

package 栈和队列;

import org.junit.Test;

import java.util.Stack;

/**
 * @Classname JZ73翻转单词序列
 * @Description TODO
 * @Date 2022/2/2 9:22
 * @Created by xjl
 */
public class JZ73翻转单词序列 {
    public String ReverseSentence(String str) {
        StringBuilder result = new StringBuilder();
        String[] s = str.split(" ");
        for(int i=s.length-1;i>=0;i--){
            result.append(s[i]).append(" ");
        }
        return result.toString().trim();
    }

    @Test
    public void test() {
        String str = "nowcoder. a am I";
        String s = ReverseSentence(str);
        System.out.println(s);
    }
}

2.5 滑动串口的最大值

滑动窗口的最大值_牛客题霸_牛客网

第一种，硬暴力

2.6

2.7

博文参考