• 1989

## Learning Opportunities

This puzzle can be solved using the following concepts. Practice using these concepts and improve your skills.

## Goal

You get a sudoku grid from a player and you have to check if it has been correctly filled.

A sudoku grid consists of 9×9 = 81 cells split in 9 sub-grids of 3×3 = 9 cells.
For the grid to be correct, each row must contain one occurrence of each digit (1 to 9), each column must contain one occurrence of each digit (1 to 9) and each sub-grid must contain one occurrence of each digit (1 to 9).

You shall answer true if the grid is correct or false if it is not.
Input
9 rows of 9 space-separated digits representing the sudoku grid.
Output
true or false
Constraints
For each digit n in the grid: 1 ≤ n ≤ 9.
Example
Input
```1 2 3 4 5 6 7 8 9
4 5 6 7 8 9 1 2 3
7 8 9 1 2 3 4 5 6
9 1 2 3 4 5 6 7 8
3 4 5 6 7 8 9 1 2
6 7 8 9 1 2 3 4 5
8 9 1 2 3 4 5 6 7
2 3 4 5 6 7 8 9 1
5 6 7 8 9 1 2 3 4```
Output
`true`

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