Java重修第十天—代码进阶

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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targetwhile (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);}
}

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