159 lines
3.9 KiB
Java
159 lines
3.9 KiB
Java
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package Others;
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class Sudoku
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{
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public static boolean isSafe(int[][] board,
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int row, int col,
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int num)
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{
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// Row has the unique (row-clash)
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for (int d = 0; d < board.length; d++)
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{
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// Check if the number we are trying to
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// place is already present in
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// that row, return false;
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if (board[row][d] == num) {
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return false;
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}
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}
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// Column has the unique numbers (column-clash)
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for (int r = 0; r < board.length; r++)
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{
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// Check if the number
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// we are trying to
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// place is already present in
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// that column, return false;
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if (board[r][col] == num)
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{
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return false;
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}
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}
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// Corresponding square has
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// unique number (box-clash)
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int sqrt = (int)Math.sqrt(board.length);
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int boxRowStart = row - row % sqrt;
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int boxColStart = col - col % sqrt;
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for (int r = boxRowStart;
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r < boxRowStart + sqrt; r++)
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{
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for (int d = boxColStart;
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d < boxColStart + sqrt; d++)
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{
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if (board[r][d] == num)
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{
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return false;
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}
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}
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}
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// if there is no clash, it's safe
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return true;
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}
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public static boolean solveSudoku(
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int[][] board, int n)
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{
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int row = -1;
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int col = -1;
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boolean isEmpty = true;
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for (int i = 0; i < n; i++)
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{
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for (int j = 0; j < n; j++)
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{
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if (board[i][j] == 0)
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{
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row = i;
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col = j;
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// We still have some remaining
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// missing values in Sudoku
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isEmpty = false;
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break;
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}
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}
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if (!isEmpty) {
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break;
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}
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}
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// No empty space left
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if (isEmpty)
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{
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return true;
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}
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// Else for each-row backtrack
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for (int num = 1; num <= n; num++)
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{
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if (isSafe(board, row, col, num))
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{
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board[row][col] = num;
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if (solveSudoku(board, n))
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{
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// print(board, n);
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return true;
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}
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else
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{
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// replace it
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board[row][col] = 0;
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}
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}
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}
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return false;
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}
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public static void print(
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int[][] board, int N)
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{
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// We got the answer, just print it
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for (int r = 0; r < N; r++)
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{
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for (int d = 0; d < N; d++)
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{
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System.out.print(board[r][d]);
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System.out.print(" ");
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}
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System.out.print("\n");
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if ((r + 1) % (int)Math.sqrt(N) == 0)
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{
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System.out.print("");
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}
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}
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}
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// Driver Code
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public static void main(String args[])
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{
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int[][] board = new int[][] {
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{ 3, 0, 6, 5, 0, 8, 4, 0, 0 },
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{ 5, 2, 0, 0, 0, 0, 0, 0, 0 },
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{ 0, 8, 7, 0, 0, 0, 0, 3, 1 },
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{ 0, 0, 3, 0, 1, 0, 0, 8, 0 },
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{ 9, 0, 0, 8, 6, 3, 0, 0, 5 },
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{ 0, 5, 0, 0, 9, 0, 6, 0, 0 },
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{ 1, 3, 0, 0, 0, 0, 2, 5, 0 },
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{ 0, 0, 0, 0, 0, 0, 0, 7, 4 },
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{ 0, 0, 5, 2, 0, 6, 3, 0, 0 }
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};
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int N = board.length;
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if (solveSudoku(board, N))
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{
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// print solution
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print(board, N);
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}
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else {
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System.out.println("No solution");
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}
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}
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}
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