Top 5 Pattern Problems in C++: Crack Your Next Coding Interview

Problem #4: Diamond Pattern

🔹 1. Problem Description

The Diamond Pattern is a classic shape problem in coding interviews that tests your ability to work with:

• Symmetrical loops
• Spacing and alignment
• Loop condition manipulation
• Nested structure formatting

It's visually appealing and technically enriching, especially when you’re asked to build symmetrical shapes with precision.

✅ Objective:

Given an integer n, print a symmetrical diamond of 2n - 1 rows using *.

For example, n = 5 should print:

    *   

   * *  

  * * * 

 * * * *

* * * * *

 * * * *

  * * * 

   * *  

    *   

🔹 2. Flowchart

Start

|

|-- Input n

|

|-- Upper Half: for i = 1 to n

|     Print (n - i) spaces

|     Print (2*i - 1) stars

|

|-- Lower Half: for i = n-1 to 1

|     Print (n - i) spaces

|     Print (2*i - 1) stars

|

End

✅ Note: Spaces help center the diamond, and stars grow or shrink in odd numbers (1, 3, 5...)

🔹 3. Algorithm

🔽 Step-by-Step Approach:

1. Start
2. Input n (height of the half-diamond)
3. Loop i = 1 to n for the upper triangle
• Print n - i spaces
• Print 2*i - 1 stars
4. Loop i = n-1 down to 1 for the lower triangle
• Print n - i spaces
• Print 2*i - 1 stars
5. End

✅ Pseudocode:

Input: n

for i = 1 to n:

    print (n - i) spaces

    print (2*i - 1) stars

for i = n-1 to 1:

    print (n - i) spaces

    print (2*i - 1) stars

🔹 4. C++ Code — Diamond Pattern

#include <iostream>

using namespace std;

int main() {

    int n;

    cout << "Enter the number of rows (half height): ";

    cin >> n;

    // Upper Half

    for (int i = 1; i <= n; i++) {

        for (int space = 1; space <= n - i; space++)

            cout << " ";

        for (int star = 1; star <= 2 * i - 1; star++)

            cout << "*";

        cout << endl;

    }

    // Lower Half

    for (int i = n - 1; i >= 1; i--) {

        for (int space = 1; space <= n - i; space++)

            cout << " ";

        for (int star = 1; star <= 2 * i - 1; star++)

            cout << "*";

        cout << endl;

    }

    return 0;

}

🔹 5. Output for n = 5

    *

   ***

  *****

 *******

*********

 *******

  *****

   ***

    *

✅ Total rows = 2n - 1, with the center line being the widest.

🔹 6. Table Breakdown: Row-wise Output

🔹 7. C++ Enhancement: Spaced Stars

If you want space between each star:

for (int star = 1; star <= i; star++)

    cout << "* ";

This will output:

    *

   * *

  * * *

 * * * *

* * * * *

 * * * *

  * * *

   * *

    *

✅ Cleaner and easier to read.

🔹 8. Performance & Complexity

🔹 9. Common Pitfalls