# Program to print a Hollow Triangle inside a Triangle

• Difficulty Level : Basic
• Last Updated : 24 Nov, 2021

Given a number N(≥ 8), the task is to print a Hollow Triangle inside a Triangle pattern.
Example:

```Input: N = 9
Output:
*
*   *
*       *
*     *     *
*     * * *     *
*                   *
*                       *
*                           *
* * * * * * * * * * * * * * * * * ```

Hey! Looking for some great resources suitable for young ones? You've come to the right place. Check out our self-paced courses designed for students of grades I-XII

Start with topics like Python, HTML, ML, and learn to make some games and apps all with the help of our expertly designed content! So students worry no more, because GeeksforGeeks School is now here!

Approach: Let i be the index for rows and j be the index for columns. Then:

• For sides of outer triangle:
If the index of column(j) is equals to (N – i + 1) or (N + i – 1), then ‘*’ is printed for equal sides of outer triangle.

```if(j == (N - i + 1)
|| j == (N + i - 1) {
print('*')
}```
•
• For sides of inner triangle:
If the (index of row(i) is less than (N – 4) and greater than (4) and index of column(j) is equals to (N – i + 4) or (N + i + 4), then ‘*’ is printed for equal sides of inner triangle.

```if(  (i >= 4
&& i <= n - 4)
&& (j == N - i + 4
|| j == N + i - 4) ) {
print('*')
}```
•
• For bases of the outer triangle:
If the index of row(i) is equal to N, then ‘*’ is printed for the base of outer triangle.

```if(i == N) {
print('*')
}```
•
• For bases of the inner triangle:
If the index of row(i) is equals (N – 4) and the column index(j) must be greater than equals to (N – (N – 2*4)), and j is less than equals to (N + N – 2*4), then ‘*’ is printed for the base of inner triangle.

```if( (i == N - 4)
&& (j >= N - (N - 2 * 4) )
&& (j <= n + n - 2 * 4) ) ) {
print('*')
}```
•

Below is the implementation of the above approach:

## CPP

 `// C++ implementation of the above approach` `#include ``using` `namespace` `std;` `// Function to print the pattern``void` `printPattern(``int` `n)``{` `    ``int` `i, j;` `    ``// Loop for rows``    ``for` `(i = 1; i <= n; i++) {` `        ``// Loop for column``        ``for` `(j = 1; j < 2 * n; j++) {` `            ``// For printing equal sides``            ``// of outer triangle``            ``if` `(j == (n - i + 1)``                ``|| j == (n + i - 1)) {``                ``cout << ``"* "``;``            ``}` `            ``// For printing equal sides``            ``// of inner triangle``            ``else` `if` `((i >= 4 && i <= n - 4)``                     ``&& (j == n - i + 4``                         ``|| j == n + i - 4)) {` `                ``cout << ``"* "``;``            ``}` `            ``// For printing base``            ``// of both triangle``            ``else` `if` `(i == n``                     ``|| (i == n - 4``                         ``&& j >= n - (n - 2 * 4)``                         ``&& j <= n + n - 2 * 4)) {` `                ``cout << ``"* "``;``            ``}` `            ``// For spacing between the triangle``            ``else` `{``                ``cout << ``" "``                     ``<< ``" "``;``            ``}``        ``}``        ``cout << ``"\n"``;``    ``}``}` `// Driver Code``int` `main()``{``    ``int` `N = 9;` `    ``printPattern(N);``}`

## Java

 `// Java implementation of the above approach``import` `java.util.*;` `class` `GFG{`` ` `// Function to print the pattern``static` `void` `printPattern(``int` `n)``{`` ` `    ``int` `i, j;`` ` `    ``// Loop for rows``    ``for` `(i = ``1``; i <= n; i++) {`` ` `        ``// Loop for column``        ``for` `(j = ``1``; j < ``2` `* n; j++) {`` ` `            ``// For printing equal sides``            ``// of outer triangle``            ``if` `(j == (n - i + ``1``)``                ``|| j == (n + i - ``1``)) {``                ``System.out.print(``"* "``);``            ``}`` ` `            ``// For printing equal sides``            ``// of inner triangle``            ``else` `if` `((i >= ``4` `&& i <= n - ``4``)``                     ``&& (j == n - i + ``4``                         ``|| j == n + i - ``4``)) {`` ` `                ``System.out.print(``"* "``);``            ``}`` ` `            ``// For printing base``            ``// of both triangle``            ``else` `if` `(i == n``                     ``|| (i == n - ``4``                         ``&& j >= n - (n - ``2` `* ``4``)``                         ``&& j <= n + n - ``2` `* ``4``)) {`` ` `                ``System.out.print(``"* "``);``            ``}`` ` `            ``// For spacing between the triangle``            ``else` `{``                ``System.out.print(``" "``                    ``+ ``" "``);``            ``}``        ``}``        ``System.out.print(``"\n"``);``    ``}``}`` ` `// Driver Code``public` `static` `void` `main(String[] args)``{``    ``int` `N = ``9``;`` ` `    ``printPattern(N);``}``}` `// This code is contributed by sapnasingh4991`

## Python3

 `# Python3 implementation of the above approach` `# Function to print the pattern``def` `printPattern(n):` `    ``# Loop for rows``    ``for` `i ``in` `range``(``1``, n ``+` `1``):` `        ``# Loop for column``        ``for` `j ``in` `range``(``1``, ``2` `*` `n):` `            ``# For printing equal sides``            ``# of outer triangle``            ``if` `(j ``=``=` `(n ``-` `i ``+` `1``)``                ``or` `j ``=``=` `(n ``+` `i ``-` `1``)):``                ``print``(``"* "``,end``=``"")` `            ``# For printing equal sides``            ``# of inner triangle``            ``elif` `((i >``=` `4` `and` `i <``=` `n ``-` `4``)``                    ``and` `(j ``=``=` `n ``-` `i ``+` `4``                        ``or` `j ``=``=` `n ``+` `i ``-` `4``)):` `                ``print``(``"* "``,end``=``"")` `            ``# For printing base``            ``# of both triangle``            ``elif` `(i ``=``=` `n``                    ``or` `(i ``=``=` `n ``-` `4``                        ``and` `j >``=` `n ``-` `(n ``-` `2` `*` `4``)``                        ``and` `j <``=` `n ``+` `n ``-` `2` `*` `4``)):` `                ``print``(``"* "``, end``=``"")` `            ``# For spacing between the triangle``            ``else` `:``                ``print``(``" "``+``" "``, end``=``"")` `        ``print``()` `# Driver Code``N ``=` `9` `printPattern(N)` `# This code is contributed by mohit kumar 29`

## C#

 `// C# implementation of the above approach``using` `System;` `class` `GFG{``  ` `// Function to print the pattern``static` `void` `printPattern(``int` `n)``{``  ` `    ``int` `i, j;``  ` `    ``// Loop for rows``    ``for` `(i = 1; i <= n; i++) {``  ` `        ``// Loop for column``        ``for` `(j = 1; j < 2 * n; j++) {``  ` `            ``// For printing equal sides``            ``// of outer triangle``            ``if` `(j == (n - i + 1)``                ``|| j == (n + i - 1)) {``                ``Console.Write(``"* "``);``            ``}``  ` `            ``// For printing equal sides``            ``// of inner triangle``            ``else` `if` `((i >= 4 && i <= n - 4)``                     ``&& (j == n - i + 4``                         ``|| j == n + i - 4)) {``  ` `                ``Console.Write(``"* "``);``            ``}``  ` `            ``// For printing base``            ``// of both triangle``            ``else` `if` `(i == n``                     ``|| (i == n - 4``                         ``&& j >= n - (n - 2 * 4)``                         ``&& j <= n + n - 2 * 4)) {``  ` `                ``Console.Write(``"* "``);``            ``}``  ` `            ``// For spacing between the triangle``            ``else` `{``                ``Console.Write(``" "``                    ``+ ``" "``);``            ``}``        ``}``        ``Console.Write(``"\n"``);``    ``}``}``  ` `// Driver Code``public` `static` `void` `Main(String[] args)``{``    ``int` `N = 9;``  ` `    ``printPattern(N);``}``}` `// This code is contributed by 29AjayKumar`

## Javascript

 ``
Output:
```                *
*   *
*       *
*     *     *
*     * * *     *
*                   *
*                       *
*                           *
* * * * * * * * * * * * * * * * *```

Time Complexity: O(n2)

Auxiliary Space: O(1)

My Personal Notes arrow_drop_up