Beginner: Patterns 2 & Introduction to Strings

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Agenda

1. Print reverse triangle V
2. Print numeric triangle /\
3. Strings
4. next() vs nextLine()
5. How to deal with different type of inputs
6. Character Pattern

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Problem Statement

Print the following pattern:

For example,

N = 5

* * * * *
 * * * *
  * * *
   * *  
    *

N = 4

* * * *
 * * *
  * *
   *

Warning

Please take some time to think about the solution approach on your own before reading further.....

Observation

Lets consider the spaces as "_"

* _ * _ * _ * _ * _
_ * _ * _ * _ * _
_ _ * _ * _ * _ 
_ _ _ * _ * _ 
_ _ _ _ * _ 

Now lets assume we are removing the spaces after every '*', then

* * * * *
_ * * * *
_ _ * * * 
_ _ _ * * 
_ _ _ _ * 

While printing stars, remember to print a space after every star, to get the our required reverse triangle pattern.

Code

for (int i = 0; i < N; i++) {

   //loop to print i spaces
    for (int j = 1; j <= i; j++) {
        System.out.print(" ");
    }

    //loop to print n-i stars
    for (int j = 1; j <= n - i; j++) {
        System.out.print("* ");
    }

    System.out.println();
}

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Problem Statement

Print the following pattern:

For example,

N = 5

0 0 0 0 1 0 0 0 0 
0 0 0 2 3 2 0 0 0 
0 0 3 4 5 4 3 0 0 
0 4 5 6 7 6 5 4 0 
5 6 7 8 9 8 7 6 5 

N = 4

0 0 0 1 0 0 0  
0 0 2 3 2 0 0  
0 3 4 5 4 3 0  
4 5 6 7 6 5 4  

Warning

Please take some time to think about the solution approach on your own before reading further.....

Approach

Lets divide the pattern into two halfs,

Lets consider the 2 halves separately,

First Half

0	0	0	0	1
0	0	0	2	3
0	0	3	4	5
0	4	5	6	7
5	6	7	8	9

Lets create a table, on observing the pattern.

row	zeros	start	end
1	4 [5-1]	1	1 [2*1-1]
2	3 [5-2]	2	3 [2*2-1]
3	2 [5-3]	3	5 [2*3-1]
4	1 [5-4]	4	7 [2*4-1]
5	0 [5-5]	5	9 [2*5-1]

We can come up with an generalized pattern on observing the values of the table based on the value i.

ith row	(n - i) zeros	starts with i	ends with 2 * i - 1

Psuedo code for First Half

// Printing (n - i) zeros
for (int j = 1; j <= n - i; j++){
    System.out.print(0 + " ");
}

int lim = 2 *i - 1;
// Printing the increasing numbers from i to 2*i-1
for (int j = i; j <= lim; j++){
    System.out.print(j + " ");
}

Second Half

0	0	0	0
2	0	0	0
4	3	0	0
6	5	4	0
8	7	6	5

Lets create a table, on observing the pattern.

row	start	end	zeros
1			4
2	2 [2*2-2]	2	3
3	4 [2*3-2]	3	2
4	6 [2*4-2]	4	1
5	8 [2*5-2]	5	0

We can come up with an generalized pattern on observing the values of the table based on the value i.

ith row	starts with (i * 2 - 2)	ends with i	(n i) zeros

Here starts with (i * 2 - 2) can be even simplified, by using the end value of the previous calculation as end - 1.

Psuedo code for Second Half

// For the Second Half
// Printing the decreasing numbers
int lim = 2 *i - 1;
for (int j = lim - 1; j >= i; j--){
    System.out.print(j + " ");
}

//loop to print n - i zeros
for (int j = 1; j <= n - i; j++){
    System.out.print(0 + " ");
}

Overall Code

for (int i = 1; i <= n; i++){

    // For the First Half
    //loop to print n - i zeros
    for (int j = 1; j <= n - i; j++){
        System.out.print(0 + " ");
    }

    int lim = 2 *i - 1;
    // Printing the increasing numbers from i to 2*i-1
    for (int j = i; j <= lim; j++){
        System.out.print(j + " ");
    }

    // For the Second Half
    // Printing the decreasing numbers
    for (int j = lim - 1; j >= i; j--){
        System.out.print(j + " ");
    }

    //loop to print n - i zeros
    for (int j = 1; j <= n - i; j++){
        System.out.print(0 + " ");
    }

    System.out.println();
}

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Reading Inputs for Strings

1. sc.next()-> cannot take spaces as input

Ques1:

Input: "Hello World"
String s1 = sc.next();
System.out.println(s1);

String s2 = sc.next(); 
System.out.println(s2);

Output:

Hello
World

Explanation:

s1 will have first word, Hello

s2 will have next word, World

2. sc.nextLine() -> can take spaces as well, until next line is encountered.

Ques1:

Input: Hello World
String s3 = sc.nextLine();
System.out.println(s3);

Output:

Hello World

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Question

Input :

Hello World

Scanner scn = new Scanner(System.in);
String str1 = scn.next(); 
String str2 = scn.next(); 
System.out.println(str1);
System.out.println(str2);

Choices

• Hello
  World
• Hello
• World
• None of the above

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Output:

Hello
World

Explanation:

str1 will have, Hello

str2 will have next word, World

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Question

Input:

Hello Welcome in Robin Dhole blog

Scanner scn = new Scanner(System.in);
String str1 = scn.next(); 
String str2 = scn.nextLine(); 
System.out.println(str1);
System.out.println(str2);   

Choices

• Hello
• Error
• Hello
  Welcome in Robin Dhole blog
• None of the above

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Output:

Hello
Welcome in Scaler

Explanation:

str1 will have first word, Hello

str2 will have complete line after hello, Welcome in Robin Dhole blog(including space before welcome).

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Rule: When the inputs are given in separate lines, and we take a String input using nextLine() after taking number input[nextInt(), nextLong(), nextFloat(), nextDouble()] or a single word [next()] then we get a empty String.

Example

Input

45
Hello World!

Scanner sc = new Scanner(System.in);
int x = sc.nextInt(); // x[45]
String st = sc.nextLine(); // st -> Empty String
String st2 = sc.nextLine(); // st2 -> "Hello World!"
System.out.println(st); 
System.out.println(s2); 

Output

Hello World!

Question

Predict the output :

Input- 
11
Super Excited!

Scanner scn = new Scanner(System.in);
int x = scn.nextInt();
String str = scn.nextLine();
System.out.println(x);
System.out.println(str);    

Choices

• 11 Super Excited!
• Error
• 11
  Super Excited!
• 11

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Question

Predict the output :

Input- 
11
Super Excited!

Scanner scn = new Scanner(System.in);
int x = scn.nextInt();
String str = scn.nextLine();
System.out.println(x);
System.out.println(str);
System.out.println("The End");  

Choices

• 11 Super Excited! The End
• 11
  The End
• Error
• 11
  Super Excited!
  The End

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Character:

A character represent a single symbol.

There are different types of characters:

• Uppercase characters : ['A' - 'Z']
• Lowercase characters : ['a' - 'z']
• Numeric characters: ['0' - '9']
• Special characters: ['@', '#', '$', '%', '&'...]

There are a total of 128 characters.

Syntax

Example 1:

char ch = 'a';
System.out.println(ch);

Output:

a

Example 2:

char ch = 'ab';
System.out.println(ch);

Output:

Error: Only a single symbol is a character.

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Problem Statement

Write a program to print all characters from A to Z.

Code

public static void printCharacters(String str) {
    for(char i = 'A'; i <= 'Z'; i++) {
        System.out.println(i);
    } 
}

Character Stairacase Pattern

N = 5

A 
A B 
A B C 
A B C D 
A B C D E 

N = 3

A 
A B 
A B C 

Warning

Please take some time to think about the solution approach on your own before reading further.....

Approach

Consider the spaces as underscores (for better visualization).

Lets take N = 5,

A _ 
A _ B _ 
A _ B _ C _ 
A _ B _ C _ D _ 
A _ B _ C _ D _ E _ 

Lets assume we are printing the standard stair case pattern,

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5

Now both the patterns is similar. So, instead of printing numbers, we just create a new variable, which starts with A, then increment inside the innerloop.

Code

for (int i = 1; i <= N; ++i) {
    char ch = 'A';
    for (char j = 1; j <= i; j++) {
        System.out.print(ch + " ");
        ch++;
    }
    System.out.println();
}

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