NC_111_MAXVALUE NC_113_CHECK_IP NC_119_SMALLEST_K

package org.example.interview.practice;

import java.util.Arrays;

/**
 * @author xianzhe.ma
 * @date 2021/8/14
 */

public class NC_111_MAXVALUE {

    public String solve (int[] nums) {
        // write code here
        if(nums == null || nums.length == 0)
            return "";
        int n = nums.length;
        String[] strs = new String[n];
        for(int i = 0; i < n; i++){
            strs[i] = nums[i]+"";
        }
        Arrays.sort(strs,(s1, s2)->{
            return (s2+s1).compareTo(s1+s2);  /*降序排序*/
        });

        if(strs[0].equals("0"))
            return "0";
        StringBuffer sb = new StringBuffer();
        for(String num:strs)
            sb.append(num);
        return sb.toString();
    }
}

package org.example.interview.practice;

/**
 * @author xianzhe.ma
 * @date 2021/11/6
 */

public class NC_113_CHECK_IP {
    public static String solve (String IP) {
        // write code here
        if (IP.contains(".")) {
            String[] array = IP.split("\\.");
            if (array == null || array.length != 4) {
                return "Neither";
            }

            String mode = "[0-9]*";

            for (String str : array) {
                if (str.startsWith("0") || str.startsWith("00") || str.equals("000")) {
                    return "Neither";
                }

                if (!str.matches(mode)) {
                    return "Neither";
                }

                if (Integer.valueOf(str).compareTo(Integer.valueOf(255)) > 0) {
                    return "Neither";
                }
            }

            return "IPv4";
        }

        String mode = "[0-9]*[A-F]*[a-f]*[0-9]*[A-F]*[a-f]*";
        if (IP.contains(":")) {
            String[] array = IP.split(":");
            if (array == null || array.length != 8) {
                return "Neither";
            }

            for (String str : array) {
                if (str.length() > 4) {
                    return "Neither";
                }

                if (!str.matches(mode)) {
                    return "Neither";
                }
            }

            return "IPv6";
        }

        return "Neither";
    }

    public static void main (String[] args) {
        String input = "2001:0db8:85a3:0:0:8A2E:0370:7334";
        solve(input);
    }
}

package org.example.interview.practice;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.PriorityQueue;

/**
 * @author xianzhe.ma
 * @date 2021/7/7
 */

public class NC_119_SMALLEST_K {

    public static ArrayList<Integer> GetLeastNumbers_Solution(int [] input, int k) {
        ArrayList<Integer> list = new ArrayList<>();
        if (input == null || input.length == 0 || k > input.length || k == 0)
            return list;
        int[] arr = new int[k];//数组下标0的位置作为哨兵，不存储数据
        //初始化数组
        for (int i = 0; i < k; i++)
            arr[i] = input[i];
        buildMaxHeap(arr, k);//构造大根堆
        for (int i = k; i < input.length; i++) {
            if (input[i] < arr[0]) {
                arr[0] = input[i];
                adjustDown(arr, 0, k);//将改变了根节点的二叉树继续调整为大根堆
            }
        }
        for (int i = 0; i < arr.length; i++) {
            list.add(arr[i]);
        }
        return list;
    }
    /**
     * @Author: ZwZ
     * @Description: 构造大根堆
     * @Param: [arr, length]  length:数组长度 作为是否跳出循环的条件
     * @return: void
     * @Date: 2020/1/30-22:06
     */
    public static void buildMaxHeap(int[] arr, int length) {
        if (arr == null || arr.length == 0 || arr.length == 1)
            return;
        for (int i = (length - 1) / 2; i >= 0; i--) {
            adjustDown(arr, i, arr.length);
        }
    }
    /**
     * @Author: ZwZ
     * @Description: 堆排序中对一个子二叉树进行堆排序
     * @Param: [arr, k, length]
     * @return:
     * @Date: 2020/1/30-21:55
     */
    public static void adjustDown(int[] arr, int k, int length) {
        int value = arr[k];//哨兵
        for (int i = 2 * k; i < length; i *= 2) {
            if (i < length - 1 && arr[i] < arr[i + 1])
                i++;//取k较大的子结点的下标
            if (i > length - 1 || value >= arr[i])
                break;
            else {
                arr[k] = arr[i];
                k = i; //向下筛选
            }
        }
        arr[k] = value;
    }

    public static void main (String[] args) {
        int[] arr = {14,5,1,6,12,7,3,8};
        ArrayList<Integer> result = GetLeastNumbers_Solution2(arr, 4);
        System.out.println(result.toString());
    }

    public static ArrayList<Integer> GetLeastNumbers_Solution2(int [] input, int k) {
        ArrayList<Integer> list = new ArrayList<>();
        if (input == null || input.length == 0 || k > input.length || k == 0)
            return list;

        PriorityQueue<Integer> priorityQueue = new PriorityQueue<>(k, new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o2-o1;
            }
        });

        //初始化数组
        for (int value : input) {
            priorityQueue.add(value);
        }

        for (int i=k;i<input.length;i++) {
            priorityQueue.poll();
        }

        for (Integer value : priorityQueue) {
            list.add(value);
        }
        return list;
    }
}