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 classesimport java.io.*;// Main classclass 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--; } }} |
*************
***********
*********
*******
*****
***
*
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 loopimport 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(""); }}} |
*************
***********
*********
*******
*****
***
*
Example 3: Using do-while Loop
Java
// Java program to Print Reverse Pyramid Star Pattern// Using do-while loop// Importing input output classesimport java.io.*;// Main Classpublic 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); }} |
*************
***********
*********
*******
*****
***
*
Complexity Analysis :
Time Complexity : O(N^2)
Space Complexity : O(1)
