Java重修第十天—代码进阶

第十天代码进阶，完成以下四个题目，提高编程能力。

第一题

代码实现

package cn.msf.baseJava.d_14;

import java.util.*;

public class Test1 {
    public static void main(String[] args) {

        Random r = new Random();
        ArrayList<Integer> p = new ArrayList<>();
        Map<Integer,Integer> memo = new HashMap<>();
        for (int i = 0; i < 100;) {
            // 1. 随机生成编号
            int num = r.nextInt(200) + 1;
            if (!memo.containsKey(num)) {
                p.add(num);
                memo.put(num,i);
                i++;
            }
        }
        // 2.循环删除奇数位置
        boolean flag = true;
        while (flag) {
            ArrayList<Integer> temp = new ArrayList<>();

            for (int i = 0; i < p.size(); i++) {
                if ((i + 1) % 2 == 0) {
                    temp.add(p.get(i));
                }
            }
            p = temp;
            if (p.size() == 1) {
                flag = false;
            }
        }
        // 幸运者编号
        System.out.println(p.get(0));
        // 第一次所站的位置
        System.out.println(memo.get(p.get(0)));
    }
}

第二题

代码实现

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Test2 {
    public static void main(String[] args) {
        String userStrs = "" +
                "10001:张三:男:1990-01-01#" +
                "10002:李四:女:1989-01-09#" +
                "10003:王五:男:1999-09-09#" +
                "10004:刘备:男:1899-01-01#" +
                "10005:孙惜空:男:1900-01-01#" +
                "10006:张三:女:1999-01-01#" +
                "10007:刘备:女:1999-01-01#" +
                "10008:张三:女:2003-07-01#" +
                "10009:猪八戒:男:1900-01-01";
        // 业务一：解析字符串。
        List<User> users = new ArrayList<>();
        String[] split = userStrs.split("#");
        for (int i = 0; i < split.length; i++) {
            String str = split[i];
            String[] userStr = str.split(":");
            User user = new User();
            user.setId(Long.parseLong(userStr[0]));
            user.setName(userStr[1]);
            user.setGender(userStr[2]);
            DateTimeFormatter fmt = DateTimeFormatter.ofPattern("yyyy-MM-dd");
            LocalDate date = LocalDate.parse(userStr[3], fmt);
            user.setBirthday(date);
            users.add(user);
        }
//        System.out.println(users);

        // 业务2：统计名字出现的次数，封装到Map中
        Map<String, Integer> map = new HashMap<>();
        for (int i = 0; i < users.size(); i++) {
            User user = users.get(i);
            map.put(user.getName(), map.getOrDefault(user.getName(), 0) + 1);
        }
        for (Map.Entry<String, Integer> entry : map.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }


}

第三题

代码实现

import java.util.Arrays;

public class Test3 {
    public static void main(String[] args) {
        int[] nums = {};
        int target = 10;
        int[] res = binarySearch(nums, target);
        System.out.println(Arrays.toString(res));
    }

    private static int[] binarySearch(int[] nums, int target) {
        int[] ans = {-1, -1};
        int left = 0;
        int right = nums.length;
        boolean flag = true;
        // 找到最左边的target，
        while (left < right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] == target) {
                right = mid;
                flag = false;
            } else if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] > target) {
                right = mid;
            }
        }
        if (flag) {
            return ans;
        }

        ans[0] = left;

        left = 0;
        right = nums.length;
        // 找到最右边的target
        while (left < right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] == target) {
                left = mid + 1;
            } else if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] > target) {
                right = mid;

            }
        }
        ans[1] = left - 1;
        return ans;
    }
}

第四题

代码实现

package cn.msf.baseJava.d_14;

public class Test4 {
    public static void main(String[] args) {
        MyLinkedList<Integer> linkedList  = new MyLinkedList<Integer>();
        linkedList.add(1);
        linkedList.add(2);
        linkedList.add(3);
        linkedList.add(4);
        linkedList.add(5);
        linkedList.reverse(2,5);
        linkedList.forEach();
    }
}


class MyLinkedList<E> {
    int size;
    Node<E> head = null;

    private static class Node<E> {

        public Node() {
        }

        public E data;
        public Node<E> next;

        public Node(E data, Node<E> next) {
            this.data = data;
            this.next = next;
        }
    }

    public void add(E e) {
        if (head == null) {
            head = new Node<>(e, null);
        } else {
            Node<E> temp = head;
            while (temp.next != null) {
                temp = temp.next;
            }
            temp.next = new Node<>(e, null);

        }
        size++;
    }


    public Node<E> reverse(int left, int right) {
        if (head == null || left >= right || right > size || left < 1) {
            return head;
        }
        int gap = right - left;

        Node<E> dummy = new Node<>();
        dummy.next = head;
        Node<E> pre = dummy;
        for (int i = 0; i < left - 1; i++) {
            pre = pre.next;
        }
        Node<E> leftHead = pre;
        Node<E> start = leftHead.next;
        pre = start;
        Node<E> cur = pre.next;

        while (--gap >= 0) {
            Node<E> next = cur.next;
            cur.next = pre;
            pre = cur;
            cur = next;
        }
        leftHead.next = pre;
        start.next = cur;
        head = dummy.next;
        return head;
    }

    public void forEach() {
        if (head == null) {
            System.out.println("{}");
            return;
        }
        Node<E> temp = head;
        while (temp.next != null) {
            System.out.print(temp.data + "->");
            temp = temp.next;
        }
        System.out.print(temp.data);
    }
}