Sudoku Solver

Given a 9x9 Sudoku board, your task is to fill the empty slots and return the completed Sudoku solution.

A Sudoku is a grid composed of nine 3x3 smaller grids. The challenge is to fill in the numbers from 1 to 9 such that each digit appears only once per row, column, and 3x3 grid.

Input:

N = 9 
The next nine lines represent the Sudoku grid, where each line contains 9 space-separated integers.

Note: Empty slots in the input are represented by the number 0.

Output:

Return the complete solved Sudoku grid.

Example:

Given Sudoku Puzzle:

The task is to fill the empty slots satisfying the Sudoku constraints.

Solved Sudoku:

Constraints:

• The size of the grid is fixed, N = 9.
• 0 <= ARR[i][j] <= 9
• Time Limit: 1 second

Note:

You do not need to print anything. The system will verify your solution by checking if the solution is correct or not.