Java Program to Print Reverse Pyramid Star Pattern
Last Updated :
20 Mar, 2023
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
import java.io.*;
class GFG {
public static void main(String[] args)
{
int number = 7;
int i = number, j;
while (i > 0) {
j = 0;
while (j++ < number - i) {
System.out.print(" ");
}
j = 0;
while (j++ < (i * 2) - 1) {
System.out.print("*");
}
System.out.println();
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
import java.io.*;
class GFG{
public static void main (String[] args)
{
int number = 7;
int i, j;
for(i = number; i >= 1; i--)
{
for(j = i; j < number; j++)
{
System.out.print(" ");
}
for(j = 1; j <= (2 * i - 1); j++)
{
System.out.print("*");
}
System.out.println("");
}
}
}
|
Output
*************
***********
*********
*******
*****
***
*
Example 3: Using do-while Loop
Java
import java.io.*;
public class GFG {
public static void main(String[] args)
{
int number = 7;
int i = number, j;
do {
j = 0;
do {
System.out.print(" ");
} while (j++ < number - i);
j = 0;
do {
System.out.print("*");
}
while (j++ < i * 2 - 2);
System.out.println("");
}
while (--i > 0);
}
}
|
Output
*************
***********
*********
*******
*****
***
*
Complexity Analysis :
Time Complexity : O(N^2)
Space Complexity : O(1)
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