diff --git a/challenges/sudoku/README.md b/challenges/sudoku/README.md
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+# sudoku
+
+Created by [@Divlo](https://github.com/Divlo) on 6 July 2021.
+
+## Instructions
+
+Sudoku is a logic-based, combinatorial number-placement puzzle.
+
+The objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 subgrids that compose the grid (also called "boxes", "blocks", or "regions") contains all of the digits from 1 to 9. The puzzle setter provides a partially completed grid, which for a well-posed puzzle has a single solution.
+
+You can't use the same numbers twice in a :
+
+- row
+- column
+- square of 3x3
+
+Write a program that solves the Sudoku given in input.
+
+The empty cells are represented by 0.
+
+## Source
+
+- [Wikipedia - Sudoku](https://en.wikipedia.org/wiki/Sudoku)
+
+## Examples
+
+See the `test` folder for examples of input/output.
+
+### Example 1
+
+#### Input
+
+```txt
+5 3 0 0 7 0 0 0 0
+6 0 0 1 9 5 0 0 0
+0 9 8 0 0 0 0 6 0
+8 0 0 0 6 0 0 0 3
+4 0 0 8 0 3 0 0 1
+7 0 0 0 2 0 0 0 6
+0 6 0 0 0 0 2 8 0
+0 0 0 4 1 9 0 0 5
+0 0 0 0 8 0 0 7 9
+```
+
+#### Output
+
+```txt
+5 3 4 6 7 8 9 1 2
+6 7 2 1 9 5 3 4 8
+1 9 8 3 4 2 5 6 7
+8 5 9 7 6 1 4 2 3
+4 2 6 8 5 3 7 9 1
+7 1 3 9 2 4 8 5 6
+9 6 1 5 3 7 2 8 4
+2 8 7 4 1 9 6 3 5
+3 4 5 2 8 6 1 7 9
+```
diff --git a/challenges/sudoku/solutions/.gitkeep b/challenges/sudoku/solutions/.gitkeep
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index 0000000..e69de29
diff --git a/challenges/sudoku/test/1/input.txt b/challenges/sudoku/test/1/input.txt
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+++ b/challenges/sudoku/test/1/input.txt
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+5 3 0 0 7 0 0 0 0
+6 0 0 1 9 5 0 0 0
+0 9 8 0 0 0 0 6 0
+8 0 0 0 6 0 0 0 3
+4 0 0 8 0 3 0 0 1
+7 0 0 0 2 0 0 0 6
+0 6 0 0 0 0 2 8 0
+0 0 0 4 1 9 0 0 5
+0 0 0 0 8 0 0 7 9
\ No newline at end of file
diff --git a/challenges/sudoku/test/1/output.txt b/challenges/sudoku/test/1/output.txt
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+++ b/challenges/sudoku/test/1/output.txt
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+5 3 4 6 7 8 9 1 2
+6 7 2 1 9 5 3 4 8
+1 9 8 3 4 2 5 6 7
+8 5 9 7 6 1 4 2 3
+4 2 6 8 5 3 7 9 1
+7 1 3 9 2 4 8 5 6
+9 6 1 5 3 7 2 8 4
+2 8 7 4 1 9 6 3 5
+3 4 5 2 8 6 1 7 9
\ No newline at end of file
diff --git a/challenges/sudoku/test/2/input.txt b/challenges/sudoku/test/2/input.txt
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+++ b/challenges/sudoku/test/2/input.txt
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+0 1 0 0 4 0 0 5 0
+4 0 7 0 0 0 6 0 2
+8 2 0 6 0 0 0 7 4
+0 0 0 0 1 0 5 0 0
+5 0 0 0 0 0 0 0 3
+0 0 4 0 5 0 0 0 0
+9 6 0 0 0 3 0 4 5
+3 0 5 0 0 0 8 0 1
+0 7 0 0 2 0 0 3 0
\ No newline at end of file
diff --git a/challenges/sudoku/test/2/output.txt b/challenges/sudoku/test/2/output.txt
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+++ b/challenges/sudoku/test/2/output.txt
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+6 1 9 7 4 2 3 5 8
+4 5 7 8 3 1 6 9 2
+8 2 3 6 9 5 1 7 4
+2 3 6 4 1 9 5 8 7
+5 9 1 2 7 8 4 6 3
+7 8 4 3 5 6 2 1 9
+9 6 2 1 8 3 7 4 5
+3 4 5 9 6 7 8 2 1
+1 7 8 5 2 4 9 3 6
\ No newline at end of file
diff --git a/challenges/sudoku/test/3/input.txt b/challenges/sudoku/test/3/input.txt
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+++ b/challenges/sudoku/test/3/input.txt
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+0 7 0 0 0 0 0 0 9
+5 1 0 4 2 0 6 0 0
+0 8 0 3 0 0 7 0 0
+0 0 8 0 0 1 3 7 0
+0 2 3 0 8 0 0 4 0
+4 0 0 9 0 0 1 0 0
+9 6 2 8 0 0 0 3 0
+0 0 0 0 1 0 4 0 0
+7 0 0 2 0 3 0 9 6
\ No newline at end of file
diff --git a/challenges/sudoku/test/3/output.txt b/challenges/sudoku/test/3/output.txt
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+++ b/challenges/sudoku/test/3/output.txt
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+3 7 4 1 6 8 2 5 9
+5 1 9 4 2 7 6 8 3
+2 8 6 3 9 5 7 1 4
+6 9 8 5 4 1 3 7 2
+1 2 3 7 8 6 9 4 5
+4 5 7 9 3 2 1 6 8
+9 6 2 8 7 4 5 3 1
+8 3 5 6 1 9 4 2 7
+7 4 1 2 5 3 8 9 6
\ No newline at end of file