Tutorial
March 16, 2022

HackerRank Java

You must print two lines of output

​ Print Hello, World. on the first line.
​ Print Hello, Java. on the second line.

Sample Output

​ Hello, World.
​ Hello, Java.


Just simple Ctrl + C from the question part & Ctrl + V to the code block. Done.

1
2
3
4
5
6
7
8
9
10
public class Solution 
{

    public static void main(String[] args) 
    {
        /* Enter your code here. Print output to STDOUT. Your class should be named Solution. */
        System.out.println("Hello, World.");
        System.out.println("Hello, Java.");
    }
}

3 types of print statements


A print statement is a call to the print / println method of the System.out object.

The print method takes exactly one argument;

The println method takes one or no arguments.


The arguments maybe a String which you create using the string concatenation “+” or an object, the print and println methods call that object’s toString() method to get a printable string.


Stdin and Stdout I

​ Two ways –> Scanner class OR BufferedReader class

​ Scanner: specifying Input Stream as System.in.

1
2
3
4
5
6
7
8
9
10
11
12
// create a Scanner Object named scan
Scanner scan = new Scanner(System.in);

// use Scanner scan to read a String and an int 
String myString = scan.next();
int myInt = scan.nextInt();

// close Scanner Object because no more input to read
scan.close();

System.out.println("myString is: " + myString);
System.out.println("myInt is: " + myInt);

BufferedReader

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
FileReader fr = new FileReader("File.txt");
// or use InputStreamReader
// InputStreamReader insreader =new InputStreamReader(System.in); 

// create a BufferedReader Object
BufferedReader bfreader = new BufferedReader(fr);

String name="";    
while(!name.equals("stop"))
{
    System.out.println("Enter data: ");    
    name = bfreader.readLine();    
    System.out.println("data is: "+ name);    
}              

bfreader.close();    
fr.close();   

bfreader.close();

Read integers from stdin and then print them to stdout. Each integer must be printed on a new line.

Sample Input

42

100

125

Sample Output

42

100

125

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
import java.util.*;

public class Solution {

    public static void main(String[] args) 
    {
        Scanner scan = new Scanner(System.in);
        int a = scan.nextInt();
        int b = scan.nextInt();
        int c = scan.nextInt();
        // Complete this line
        // Complete this line

        System.out.println(a);
        System.out.println(b);
        System.out.println(c);
        // Complete this line
        // Complete this line
        
        
        
        // BETTER IDEA
        Scanner sc = new Scanner(System.in);
        while(sc.hasNextInt())
        {
            int a = sc.nextInt();
            System.out.println(a);
        }
        
        // IDEA 2
        /* 
        a Try with Resource to automatically close any classes that 
        implements AutoClosable interface (Scanner class in this case). 
        That way you don't have to do scanner.close() 
        */
        try(Scanner scan = new Scanner(System.in)) 
        {
            while (scan.hasNext())
            {
                System.out.println(scan.nextInt());
            }
        }
    }
}

获取数据类型的取值范围

1
2
3
4
if(a >= Short.MIN_VALUE && a <= Short.MAX_VALUE)
{
    System.out.println(“It’s a short type”);
}

int to String

1
2
int n = 3;
String s = String.valueOf(n);

Static Initializer Block

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
public class Solution
{
    static Scanner scan = new Scanner(System.in);
    static int breadth = scan.nextInt();
    static int height = scan.nextInt();
    
    public static void main(String[] args)
    {
    
    }
    
    static
    {
        if(breadth > 0 && height > 0)
        {
            System.out.println(breadth*height);
        }
        else
        {
            System.out.println(“java.lang.Exception: Breadth and height must be positive”);
        }
    }
}


Get day of the week based on a specific date

Input: 08 05 2015

1
2
3
4
5
6
7
import java.time.LocalDate;

public static String findDay(int month, int day, int year)
{
    LocalDate local = LocalDate.of(year, month, day);
    return local.getDayOfWeek().toString();
}

Output: WEDNESDAY


Read in content by parts(separate by space)

Input: 08 05 2015

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
public class Solution {
    public static void main(String[] args) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        String[] firstMultipleInput = bufferedReader.readLine().replaceAll("\\s+$", "").split(" ");

        int month = Integer.parseInt(firstMultipleInput[0]);

        int day = Integer.parseInt(firstMultipleInput[1]);

        int year = Integer.parseInt(firstMultipleInput[2]);

        String res = Result.findDay(month, day, year);

        bufferedWriter.write(res);
        bufferedWriter.newLine();

        bufferedReader.close();
        bufferedWriter.close();
    }
}

Currency Format

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double payment = scanner.nextDouble();
        scanner.close();


        NumberFormat f1 = NumberFormat.getCurrencyInstance(Locale.US);
        NumberFormat f2 = NumberFormat.getCurrencyInstance(new Locale("en", "IN"));
        NumberFormat f3 = NumberFormat.getCurrencyInstance(Locale.CHINA);
        NumberFormat f4 = NumberFormat.getCurrencyInstance(Locale.FRANCE);
        
        String us = f1.format(payment);
        String india = f2.format(payment);
        String china = f3.format(payment);
        String france = f4.format(payment);
        
        
        System.out.println("US: " + us);
        System.out.println("India: " + india);
        System.out.println("China: " + china);
        System.out.println("France: " + france);
    }
}

String manipulation

Input:
hello
java

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
import java.io.*;
import java.util.*;

public class Solution {

    public static void main(String[] args) {
        
        Scanner sc=new Scanner(System.in);
        String A=sc.next();
        String B=sc.next();
        /* Enter your code here. Print output to STDOUT. */
        // Task 1
        System.out.println(A.length()+B.length());
        
        // Task 2
        // Compare first letter which is in front
        if(A.charAt(0) > B.charAt(0))
        {
            System.out.println("Yes");
        }
        else
        {
            System.out.println("No");
        }
        
        // Task 3
        // Replace first character with upper case
        System.out.println(
        A.replace(A.charAt(0), Character.toUpperCase(A.charAt(0))) 
        + " " 
        + B.replace(B.charAt(0), Character.toUpperCase(B.charAt(0))));
    }
}

Output:
9
No
Hello Java

Substring

Syntax: substring(startInx, endInx)

1
2
String s = “HelloWorld”;
System.out.println(s.substring(1,4));

Output:
ello


char to String

1
2
char c = ‘M’;
String s = Character.toString(c);

Convert String array to char array

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
public class CharArrayDemo4 
{  
    public static void main(String[] args) 
    {  
        String value = "JavaTPoint";  
        
        //Convert string to a char array.  
        char[] array = value.toCharArray();
    
        for(char c : array)  
        {  
            System.out.println(c);  
        }  
    }  
}

Java Palindrome(String reverse)

Palindrome explanation:
If a word/sentence read the same either from the front to end or end to front, then it is a palindrome word/sentence.

Eg. madam is a palindrome word.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
import java.io.*;
import java.util.*;

public class Solution 
{

    public static void main(String[] args) 
    {
        Scanner sc = new Scanner(System.in);
        String A = sc.next();
        
        int capacity = A.length();
        char[] list1 = new char[capacity];
        char[] list2 = new char[capacity];
        
        for(int i = 0; i < A.length(); i++)
        {
            list1[i] = A.charAt(i);
        }
        
        int index = 0;
        for(int j = capacity-1; j >= 0; j--)
        {
            list2[index] = A.charAt(j);
            index++;
        }
        
        if(Arrays.equals(list1, list2))
        {
            System.out.println("Yes");
        }
        else
        {
            System.out.println("No");
        }
    }
}

Better Solution

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
import java.io.; 
import java.util.;

public class Solution 
{
    public static void main(String[] args) 
    {
    
        String rev = " ";
        Scanner sc = new Scanner(System.in);
        String A = sc.next();
    
        for (int i = A.length()-1; i >= 0; i--) 
        {
            rev += A.charAt(i); 
        }

        if (A.equals(rev.trim()))
        {
            System.out.println("Yes");       
        }
        else
        {
            System.out.println("No");
        }
    }
}

注：这里没必要加.trim(), 把rev定义为””就好。
trim()的目的是去掉一段String的开头和结尾处的空白。


replaceAll Regex Example

regex内特殊字符用[]包括即可。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
import java.io.*;
import java.util.*;

public class Solution {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String s = scan.nextLine();
        // Write your code here.
        
        String[] parts = s.replaceAll("[ !._@,'?]"," ").split(" ");
        
        int num = 0;
        for(String sss : parts)
        {
            if(sss.length() != 0)
            {
                num++;
            }
        }
        System.out.println(num);
        
        for(String ss : parts)
        {
            if(ss.length() == 0)
            {
                continue;
            }
            else
            {
                System.out.println(ss);
            }
            
        }
        scan.close();
    }
}

Pattern compile

Compile the given regular expression into a pattern.

1
2
3
public static Pattern compile(String regex)

// Throws PatternSyntaxException if the expression syntax is invalid.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
import java.util.Scanner;
import java.util.regex.*;

public class Solution
{
    public static void main(String[] args)
    {
        Scanner in = new Scanner(System.in);
        int testcase = Integer.parseInt(in.nextLine());
    
        while(testcase > 0)
        {
            String pattern = in.nextLine();
            
            try
            {
                Pattern check = Pattern.compile(pattern);
                System.out.println(“Valid”);
            }
            catch(PatternSyntaxException e)
            {
                System.out.println(“Invalid”);
            }
            testcase—-;
        }
    }
}


Reference

About this Post

This post is written by Andy, licensed under CC BY-NC 4.0.

#Java#HackerRank