C++ Program To Print Inverted Pyramid

Here we will build a C++ Program To Print Inverted Pyramid using 3 different approaches:

1. Half Inverted Using "*"
2. Half Inverted Using Numbers
3. Full Inverted Pyramid using " * "

1. Program to print inverted half Triangle using " * "

Input: 

n=4

Output:

* * * *
* * *
* *
*

As we can observe from the given example the number of printed rows is equal to the given input n and the number of printed columns is decreasing from n to 1. Therefore we run the outer for loop from n to 1 and the inner for loop from 1 to row number

Example: 

// C++ program to demonstrate
// inverted half triangle using *
using namespace std;
#include <bits/stdc++.h>
#include <iostream>
int main()
{
    int n = 4;
    for (int i = n; i >= 1; --i) {
        for (int j = 1; j <= i; ++j) {
            cout << "* ";
        }
        cout << endl;
    }

    return 0;
}

* * * * 
* * * 
* * 
* 

Time complexity: O(n²) 

Here n is number of rows.

Space complexity: O(1)

As constant extra space is used.

2. Program to print an inverted half pyramid using numbers

Input 

n=4

Output:

1 2 3 4
1 2 3
1 2
1

By looking at the given example we can try to run the outer for loop from n to 1 and for each row traversal, we should print the elements from 1 to the row number. This means instead of printing * we need to print that specific column number.

Example: 

// C++ program to demonstrate
// inverted half triangle using Digits
using namespace std;
#include <bits/stdc++.h>
#include <iostream>
int main()
{
    int n=4; // took a default value
    for (int i = n; i >= 1; --i) { // loop for iterating
        for (int j = 1; j <= i; ++j) { // loop for printing
            cout << j << " ";
        }
        cout << endl;
    }
    return 0;
}

1 2 3 4 
1 2 3 
1 2 
1 

Time complexity: O(n²)

Here n is number of rows.

Space complexity: O(1)

As constant extra space is used.

3. Program to print inverted full pyramid using " * "

Input:

n = 4

Output:

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

Example: 

// C++ program to demonstrate
// inverted pyramid using *
using namespace std;
#include <bits/stdc++.h>
#include <iostream>
int main()
{
    int n=5;
    for (int i = n; i >= 1; --i) {
        for (int k = 0; k < n - i; ++k) {
            cout << "  ";
        }
        for (int j = i; j <= 2 * i - 1; ++j) {
            cout << "* ";
        }
        for (int j = 0; j < i - 1; ++j) {
            cout << "* ";
        }
        cout << endl;
    }
    return 0;
}

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

Time complexity: O(n²) for given input n

Space complexity: O(1)