Create sudoku.cpp

Recursion & Backtracking/sudoku.cpp

@@ -0,0 +1,105 @@
+#include <iostream>
+
+using namespace std;
+
+
+#define N 9
+
+
+void print(int arr[N][N])
+{
+	for (int i = 0; i < N; i++)
+	{
+		for (int j = 0; j < N; j++)
+			cout << arr[i][j] << " ";
+		cout << endl;
+	}
+}
+
+
+bool isSafe(int grid[N][N], int row,
+					int col, int num)
+{
+
+
+	for (int x = 0; x <= 8; x++)
+		if (grid[row][x] == num)
+			return false;
+
+
+	for (int x = 0; x <= 8; x++)
+		if (grid[x][col] == num)
+			return false;
+
+	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;
+}
+
+
+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 <= N; num++)
+	{
+
+
+		if (isSafe(grid, row, col, num))
+		{
+
+
+			grid[row][col] = num;
+
+
+			if (solveSudoku(grid, row, col + 1))
+				return true;
+		}
+
+
+		grid[row][col] = 0;
+	}
+	return false;
+}
+
+
+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 } };
+
+	if (solveSudoku(grid, 0, 0))
+		print(grid);
+	else
+		cout << "no solution exists " << endl;
+
+	return 0;
+	// This is code is contributed by Pradeep Mondal P
+}