2020秋招笔试题目

205. 同构字符串

class Solution {
    public boolean isIsomorphic(String s, String t) {
        return isIsomorphic1(s,t)&&isIsomorphic1(t,s);
    }
    public boolean isIsomorphic1(String s, String t) {
        if (s.length() == 0) {
            return true;
        }
        HashMap<Character, Character> map = new HashMap<>();
        for (int i = 0; i < s.length(); i++) {
            if (!map.containsKey(s.charAt(i))) {
                map.put(s.charAt(i), t.charAt(i));
            } else {
                if (t.charAt(i) != map.get(s.charAt(i))) {
                    return false;
                } else {
                    continue;
                }
            }
        }
        return true;
    }

剑指 Offer 09. 用两个栈实现队列

/**
 * Copyright (C), 2018-2020
 * FileName: MyQueue
 * Author:   xjl
 * Date:     2020/8/25 12:43
 * Description: 栈实现队列
 */
package Stack;

import java.util.Stack;

/**
 * 利用的两个栈来实现的队列的
 */
public class MyQueue {
    Stack<Integer> stack1;
    Stack<Integer> stack2;

    public MyQueue() {
        stack1 = new Stack<>();
        stack2 = new Stack<>();
    }

    //插入元素
    public void push(int x) {
        //现将stack中弹出
        while (!stack1.isEmpty()) {
            stack2.add(stack1.peek());
            stack1.pop();
        }
        //插入元素
        stack1.add(x);
        //在往stack1中
        while (!stack2.isEmpty()) {
            stack1.add(stack2.peek());
            stack2.pop();
        }
    }

    public int pop() {
        return stack1.pop();
    }

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

    public boolean empty() {
        return stack1.isEmpty();
    }

    public static void main(String[] args) {
        MyQueue queue = new MyQueue();
        queue.push(1);
        queue.push(2);
        queue.push(3);
        queue.push(4);

        while (!queue.empty()) {
            System.out.println(queue.peek());
            queue.pop();
        }
    }
}

232. 用栈实现队列

/**
 * Copyright (C), 2018-2020
 * FileName: MyQueue
 * Author:   xjl
 * Date:     2020/8/25 12:43
 * Description: 栈实现队列
 */
package Stack;

import java.util.Stack;

/**
 * 利用的两个栈来实现的队列的
 */
public class MyQueue {
    Stack<Integer> stack1;
    Stack<Integer> stack2;

    public MyQueue() {
        stack1 = new Stack<>();
        stack2 = new Stack<>();
    }

    //插入元素
    public void push(int x) {
        //现将stack中弹出
        while (!stack1.isEmpty()) {
            stack2.add(stack1.peek());
            stack1.pop();
        }
        //插入元素
        stack1.add(x);
        //在往stack1中
        while (!stack2.isEmpty()) {
            stack1.add(stack2.peek());
            stack2.pop();
        }
    }

    public int pop() {
        return stack1.pop();
    }

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

    public boolean empty() {
        return stack1.isEmpty();
    }

    public static void main(String[] args) {
        MyQueue queue = new MyQueue();
        queue.push(1);
        queue.push(2);
        queue.push(3);
        queue.push(4);

        while (!queue.empty()) {
            System.out.println(queue.peek());
            queue.pop();
        }
    }
}

剑指 Offer 31. 栈的压入、弹出序列

 

剑指 Offer 30. 包含min函数的栈

 

225. 用队列实现栈

/**
 * Copyright (C), 2018-2020
 * FileName: MyStack
 * Author:   xjl
 * Date:     2020/8/25 12:59
 * Description: 队列实现栈
 */
package Stack;

import java.util.LinkedList;
import java.util.Queue;

public class MyStack {

    Queue<Integer> queue1;//存取的元素的
    Queue<Integer> queue2;//临时存放元素

    public MyStack() {
        queue1 = new LinkedList<>();
        queue2 = new LinkedList<>();
    }

    public void push(int x) {
        //检查是否无空
        while (!queue1.isEmpty()) {
            queue2.add(queue1.peek());
            queue1.poll();
        }
        //刚进来的元素
        queue1.add(x);
        while (!queue2.isEmpty()) {
            queue1.add(queue2.peek());
            queue2.poll();
        }
    }

    public int pop() {
        return queue1.poll();
    }

    public int top() {
        return queue1.peek();
    }

    public boolean empty() {
        return queue1.isEmpty();
    }

    public static void main(String[] args) {
        MyStack stack = new MyStack();
        stack.push(1);
        stack.push(2);
        stack.push(3);
        stack.push(4);

        while (!stack.empty()) {
            System.out.println(stack.top());
            stack.pop();
        }
    }

}