> For the complete documentation index, see [llms.txt](https://42-guide.gitbook.io/42-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://42-guide.gitbook.io/42-guide/piscine-life/rushes/rush01.md).

# Rush01

You need to develop a program that solves a **4x4 grid puzzle** where you must place **boxes (numbers) of heights 1 to 4** in each square. However, there are **view constraints** that determine how many boxes are visible from each row and column.

* The constraints come from **four different perspectives**:
  * Left → Right
  * Right → Left
  * Top → Bottom
  * Bottom → Top
* Each row and column must have **unique** numbers (no repetition of 1-4).

***

#### **How the Puzzle Works**

1. The program takes **16 numbers** as input. Each number represents how many boxes are visible from a given direction.
2. The goal is to place numbers (1 to 4) in the **4x4 grid** so that:
   * The number of visible boxes from each direction matches the given input.
   * No number is repeated in a single row or column.

Example:

```
Input: "4 3 2 1 1 2 2 2 4 3 2 1 1 2 2 2"
Output:
1 2 3 4
2 3 4 1
3 4 1 2
4 1 2 3
```

Here, the boxes are placed correctly based on the given constraints.

***

#### **Project Rules & Constraints**

* Your **program must compile** using:

  ```
  gcc -Wall -Wextra -Werror -o rush-01 *.c
  ```
* Allowed functions:
  * `write()`
  * `malloc()`
  * `free()`
* Any **invalid input must return an "Error" message**.
* You must **collaborate with your teammates**, and each member must understand the entire solution.
* **Submission is final**, and you must present your code during defense.

***

#### **How to Approach the Solution**

1. **Parse the Input**
   * Convert the string of numbers into an integer array.
   * Ensure it contains exactly **16 numbers (1-4).**
   * Handle errors if the input is incorrect.
2. **Grid Initialization**
   * Create a 4x4 matrix to store numbers.
3. **Backtracking Algorithm**
   * Try placing numbers (1-4) in each cell.
   * Check if the row, column, and visibility constraints are met.
   * If a placement is invalid, backtrack and try a different number.
4. **Output the Solution**
   * Print the grid in the required format.
   * If no valid solution exists, print `"Error"`.

***

#### **Next Step: Understanding the Code (without bonus)**


---

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