C++ Program To Print Triangle Pattern

Here we will see how to print triangle patterns using a C++ program. There are 4 patterns discussed here:

1. Right Triangle.
2. Inverted Right Triangle.
3. Equilateral Triangle.
4. Inverted Equilateral Triangle.
5. Inverted Mirrored Right Triangle.

Let’s start discussing each of these in detail.

1. Right Triangle

Below are the examples for the right triangle:

Input: 4
Output: 
*
* *
* * *
* * * *

Input: 5
Output: 
*
* *
* * *
* * * *
* * * * *

In the above pattern, it can be observed that

i^th row has i elements

Below is the C++ program to print the right triangle:

C++

// C++ program to print
// right triangle
#include <iostream>
using namespace std;

// Driver code
int main()
{
    int n = 5;

    // ith row has i elements
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= i; j++)
            cout << "* ";
        cout << endl;
    }
    return 0;
}

Output

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

Time Complexity: O(n^2)
Auxiliary Space: O(1)

2. Inverted Right Triangle

Below are the examples of inverted right triangles:

Input: 5
Output:
* * * * *
* * * *
* * *
* *
*

Input: 6
Output:
* * * * * *
* * * * *
* * * *
* * *
* *
*

In this example, it can be observed that if there are a total of n rows in the triangle then:

i^th row has n-i+1 elements

Below is the C++ program to print an inverted right triangle:

C++

// C++ program to print inverted
// right triangle
#include <iostream>
using namespace std;

// Driver code
int main()
{
    int n = 5;

    // ith row has n-i+1 elements
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n - i + 1; j++)
            cout << "* ";
        cout << endl;
    }
    return 0;
}

Output

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

Time Complexity: O(n^2)
Auxiliary Space: O(1)

Another Approach:

C++

// Another C++ Approach for printing
// Inverted Right Triangle
#include <bits/stdc++.h>
using namespace std;
// similar to right triangle's code
int main()
{
    int n = 5;
    // start printing from the last row, i.e., nth row
    for (int i = n; i >= 1; i--) {
        for (int j = i; j >= 1; j--)
            cout << "* ";
        cout << endl;
    }
    return 0;
}

Output

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

Time Complexity: O(n^2)
Auxiliary Space: O(1)

3. Equilateral Triangle

Below are examples of an equilateral triangle:

 Input: 5
Output:
*
   * *
  * * *
 * * * *
* * * * *

Input: 6
Output:
     *
    * *
   * * *
  * * * *
 * * * * *
* * * * * *

In this example, it can be observed that if there are n rows in the pattern then:

i^th row has i elements and has (n – i) leading spaces

Below is the C++ program to print an equilateral triangle:

C++

// C++ program to print
// equilateral triangle
#include <iostream>
using namespace std;

// Driver code
int main()
{
    int n = 5;

    // ith row has n-i leading spaces
    // and i elements
    for (int i = 1; i <= n; i++) {
        // n-i leading spaces
        for (int j = 0; j < n - i; j++)
            cout << " ";

        // i elements
        for (int j = 1; j <= i; j++)
            cout << "* ";
        cout << endl;
    }
    return 0;
}

Output

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

Time Complexity: O(n^2)
Auxiliary Space: O(1)

4. Inverted Equilateral Triangle

Below are examples of an inverted equilateral triangle:

Input: 5
Output:
* * * * *
 * * * *
  * * *
   * *
    *

Input: 6
Output:

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

It can be observed if there are n rows in the pattern then:

i^th row has n-i+1 elements and i-1 leading spaces

Below is the C++ program to print an inverted equilateral triangle:

C++

// C++ program to print an
// inverted equilateral triangle
#include <iostream>
using namespace std;

// Driver code
int main()
{
    int n = 5;

    // ith row has n-i+1 elements
    for (int i = 1; i <= n; i++) {
        // leading spaces
        for (int j = 1; j < i; j++)
            cout << " ";
        for (int j = 1; j <= n - i + 1; j++)
            cout << "* ";
        cout << endl;
    }
    return 0;
}

Output

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

Time Complexity: O(n^2)
Auxiliary Space: O(1)

Another Approach:

C++

#include <bits/stdc++.h>
using namespace std;
// similar to the equilateral triangle code
int main()
{
    int n = 5;
    // start printing from the last row, i.e., nth row
    for (int i = n; i >= 1; i--) {
        for (int j = 0; j <= n - i; j++)
            cout << " ";
        for (int j = 1; j <= i; j++)
            cout << "* ";
        cout << endl;
    }
    return 0;
}

Output

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

Time Complexity: O(n^2)
Auxiliary Space: O(1)

5. Inverted Mirrored Right Triangle

Below are the examples of inverted mirrored right triangles:

Input: 5
Output:
* * * * *
  * * * *
    * * *
      * *
        *

Input: 6
Output:
* * * * * *
  * * * * *
    * * * *
      * * *
        * *
          *

It can be observed if there are n rows in the pattern then:

i^th row has n-i+1 elements and 2*(i-1) leading spaces

Below is the C++ program to print an inverted mirrored right triangle:

C++

// C++ program to print a
// inverted mirrored right triangle
#include <iostream>
using namespace std;

// Driver code
int main()
{
    int n = 5;

    // ith row has n-i+1 elements
    for (int i = 1; i <= n; i++) {
        // leading spaces
        for (int j = 1; j < i; j++)
            cout << "  ";
        for (int j = 1; j <= n - i + 1; j++)
            cout << "* ";
        cout << endl;
    }
    return 0;
}

Output

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

Time Complexity: O(n^2)
Auxiliary Space: O(1)