Interview questions - Supplement of Huawei computer test knowledge points

HJ1 The length of the last word in the string

 while(sc.hasNextLine()

Scanner、sc.hasNext() Method
What is? Scanner？next() and hasNext() ? nextLine() and hasNextLine()?

line = line.substring(line.lastIndexOf(" ")+1);

String class substring Method
lastIndexOf Usage of

HJ2 Count the number of occurrences of a character

Pattern compile = Pattern.compile(ch,Pattern.CASE_INSENSITIVE);
 Matcher matcher = compile.matcher(str);
 while(matcher.find()

Pattern.compile Function usage
JAVA Regular expressions ：Pattern Class and Matcher Class explanation ( turn )
JAVA Regular expressions ,matcher.find() and matcher.matches() The difference between

 char[] arrs = str.toCharArray();

ToCharArray（） Usage of

HJ5 Hexadecimal conversion

String str = sc.nextLine().substring(2);
System.out.println(Integer.parseInt(str,16));

substring(int a, int b) Method can truncate a string , When there is only one parameter , The intercept range is 【a,length-1】, When there are two parameters , The intercept range is 【a,b-1】.
Integer.parseInt(String s, int a) Method can convert base , Convert string to "a" Base number , There is only one parameter s when , Convert me 10 Base number .

HJ8 Consolidated statement records

for(Map.Entry<Integer,Integer> integerIntegerEntry : map.entrySet()){
    
          System.out.println(integerIntegerEntry.getKey()+" "+integerIntegerEntry.getValue());
  }

Summary enhanced traversal ：for,list,map,set
TreeMap Detailed introduction

HJ9 Extract non duplicate integers

// Reverse order 
        StringBuilder stringBuilder = new StringBuilder(sc.nextLine()).reverse();
        String str = stringBuilder.toString();
        
        // Result set 
        StringBuilder result = new StringBuilder();
        
        for(int i = 0; i < str.length(); i++){
    
            if(str.indexOf(str.charAt(i)) == i){
    
                result.append(str.charAt(i));
            }
        }
        System.out.println(result.toString());

Java in String、StringBuffer、StringBuilder and toString Introduction to
indexOf（String.indexOf Method ）

HJ10 Character count

 set.stream().filter(c->Integer.valueOf(c) >= 0 
                            &&
                           Integer.valueOf(c) <= 127).collect(Collectors.toSet()
                            );

java list.stream().map().collect(Collectors.toList())
lambda expression ,stream、filter、collect、set、limit、findFirst、Map、mapToInt、Distinct、sort、sorted、assertEquals

HJ11 The numbers are upside down

 System.out.println(new StringBuffer(String.valueOf(number)).reverse());

String.valueOf() Use of methods

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
 BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));

int num = Integer.parseInt(bf.readLine());

String s = num + "";// Convert to string 

Integer Class parseInt and valueOf The difference between