Java Program to Print Reverse Pyramid Star Pattern

Last Updated : 20 Mar, 2023

Try it on GfG Practice

Approach:

1. Get the number of input rows from the user using Scanner Class or BufferedReader Class object.

2. Now run two loops

Outer loop to iterate through a number of rows as initialized or input is taken from reader class object in java. Now,
- Run an inner loop from 1 to 'i-1'
- Ru another inner loop from 1 to rows * 2 – (i × 2 – 1)

Illustration:

Input: number = 7   Output:  *************  ***********   *********    *******     *****      ***       *

Methods: We can print a reverse pyramid star pattern using the following methods:

Using while loop
Using for loop
Using do-while loop

Example 1: Using While Loop

Java

// Java program to Print Reverse Pyramid Star Pattern // Using While loop  // Importing input output classes import java.io.*;  // Main class class GFG {      // Main driver method     public static void main(String[] args)     {         // Declaring and initializing variable to         // Size of the pyramid         int number = 7;          int i = number, j;          // Nested while loops         // Outer loop          // Till condition holds true         while (i > 0) {             j = 0;              // Inner loop             // Condition check             while (j++ < number - i) {                 // Print whitespaces                 System.out.print(" ");             }              j = 0;              // Inner loop             // Condition check             while (j++ < (i * 2) - 1) {                 // Print star                 System.out.print("*");             }              // By now, we reach end of execution for one row             // so next line             System.out.println();              // Decrementing counter because we want to print             // reverse of pyramid             i--;         }     } }

Output

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

Steps to solve this problem:

1. Initialize the size of the pyramid 'number =7' and the variables 'i' and 'j'.

2. The outer loop will run through rows of the pyramid with 'i' starting from number and decrementing by 1 in each iteration.

3. First inner loop will start to print the gaps in each row with 'j' starting from 'i' and incrementing by 1 until it reaches number.

4. Now start second inner loop with 'j' starting at 1 and increment it by 1 until it reaches (2 * i - 1) to print the stars in each row.

5. Print new line to end each row, then repeat steps 3 through 5 until the outer loop ends.

Example 2: Using for Loop

Java

// Java program to print reverse pyramid star pattern // Using for loop import java.io.*;  class GFG{      public static void main (String[] args)  {          // Size of the pyramid     int number = 7;     int i, j;          // Outer loop handle the number of rows     for(i = number; i >= 1; i--)     {                  // Inner loop print space         for(j = i; j < number; j++)         {             System.out.print(" ");         }                  // Inner loop print star         for(j = 1; j <= (2 * i - 1); j++)         {             System.out.print("*");         }                  // Ending line after each row         System.out.println("");     }  } }

Output

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

Example 3: Using do-while Loop

Java

// Java program to Print Reverse Pyramid Star Pattern // Using do-while loop  // Importing input output classes import java.io.*;  // Main Class public class GFG {      // Main driver method     public static void main(String[] args)     {         // Declare and initialize variable to         // Size of the pyramid         int number = 7;          int i = number, j;          // Outer loop iterate until i > 0 is false         do {             j = 0;              // First inner do-while loop             do {                  // Prints space until j++ < number - i is                 // false                 System.out.print(" ");             } while (j++ < number - i);             j = 0;              // Second inner do-while loop              // Inner loop prints star             // until j++ < i * 2 - 2 is false             do {                  // print star                 System.out.print("*");             }              while (j++ < i * 2 - 2);              // Print whitespace             System.out.println("");         }          // while of outer 'do-while' loop         while (--i > 0);     } }

Output

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

Complexity Analysis :

Time Complexity : O(N^2)

Space Complexity : O(1)

Java Program to Print Upper Star Triangle Pattern

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Java Program to Print Reverse Pyramid Star Pattern

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