From f2f7180909b21c29af25b87a8fb25d4cb3d335ff Mon Sep 17 00:00:00 2001
From: Aditya Chouksey <aditychoukse@gmail.com>
Date: Fri, 24 Oct 2025 10:58:07 +0530
Subject: [PATCH] Create sudoko.cpp
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The grid uses 0 to represent empty cells.

The isSafe() function ensures no duplicates in a row, column, or 3×3 box.

The solveSudoku() uses backtracking:

Tries a number 1–9 in each empty cell.

If a number works, moves to the next cell.

If stuck, it backtracks and tries a different number.

The final grid is printed as the solution.
---
 CPP/sudoko.cpp | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 CPP/sudoko.cpp

diff --git a/CPP/sudoko.cpp b/CPP/sudoko.cpp
new file mode 100644
index 00000000..276b7bd9
--- /dev/null
+++ b/CPP/sudoko.cpp
@@ -0,0 +1,86 @@
+#include <iostream>
+using namespace std;
+
+#define N 9
+
+// Function to print the Sudoku grid
+void printGrid(int grid[N][N]) {
+    for (int row = 0; row < N; row++) {
+        for (int col = 0; col < N; col++) {
+            cout << grid[row][col] << " ";
+        }
+        cout << endl;
+    }
+}
+
+// Check if placing num in grid[row][col] is valid
+bool isSafe(int grid[N][N], int row, int col, int num) {
+    // Check row
+    for (int x = 0; x < N; x++)
+        if (grid[row][x] == num)
+            return false;
+
+    // Check column
+    for (int x = 0; x < N; x++)
+        if (grid[x][col] == num)
+            return false;
+
+    // Check 3x3 subgrid
+    int startRow = row - row % 3, startCol = col - col % 3;
+    for (int i = 0; i < 3; i++)
+        for (int j = 0; j < 3; j++)
+            if (grid[i + startRow][j + startCol] == num)
+                return false;
+
+    return true;
+}
+
+// Recursive backtracking function to solve Sudoku
+bool solveSudoku(int grid[N][N], int row, int col) {
+    if (row == N - 1 && col == N)
+        return true;
+    if (col == N) {
+        row++;
+        col = 0;
+    }
+    if (grid[row][col] != 0)
+        return solveSudoku(grid, row, col + 1);
+
+    for (int num = 1; num <= 9; num++) {
+        if (isSafe(grid, row, col, num)) {
+            grid[row][col] = num;
+            if (solveSudoku(grid, row, col + 1))
+                return true;
+            grid[row][col] = 0; // backtrack
+        }
+    }
+    return false;
+}
+
+// Main Function
+int main() {
+    int grid[N][N] = {
+        {3, 0, 6, 5, 0, 8, 4, 0, 0},
+        {5, 2, 0, 0, 0, 0, 0, 0, 0},
+        {0, 8, 7, 0, 0, 0, 0, 3, 1},
+        {0, 0, 3, 0, 1, 0, 0, 8, 0},
+        {9, 0, 0, 8, 6, 3, 0, 0, 5},
+        {0, 5, 0, 0, 9, 0, 6, 0, 0},
+        {1, 3, 0, 0, 0, 0, 2, 5, 0},
+        {0, 0, 0, 0, 0, 0, 0, 7, 4},
+        {0, 0, 5, 2, 0, 6, 3, 0, 0}
+    };
+
+    cout << "Original Sudoku Puzzle:\n";
+    printGrid(grid);
+    cout << endl;
+
+    if (solveSudoku(grid, 0, 0)) {
+        cout << "Solved Sudoku:\n";
+        printGrid(grid);
+    } else {
+        cout << "No solution exists!";
+    }
+
+    return 0;
+}