/****************************************************************************** * Compilation: javac MagicSquare.java * Execution: java MagicSquare n * * Generates a magic square of order n. A magic squares is an n-by-n * matrix of the integers 1 to n^2, such that all row, column, and * diagonal sums are equal. * * One way to generate a magic square when n is odd is to assign * the integers 1 to n^2 in ascending order, starting at the * bottom, middle cell. Repeatedly assign the next integer to the * cell adjacent diagonally to the right and down. If this cell * has already been assigned another integer, instead use the * cell adjacently above. Use wrap-around to handle border cases. * * * % java MagicSquare 3 * 4 9 2 * 3 5 7 * 8 1 6 * * % java MagicSquare 5 * 11 18 25 2 9 * 10 12 19 21 3 * 4 6 13 20 22 * 23 5 7 14 16 * 17 24 1 8 15 * * Limitations * ----------- * - n must be odd * ******************************************************************************/ public class MagicSquare { public static void main(String[] args) { int n = Integer.parseInt(args[0]); if (n % 2 == 0) throw new RuntimeException("n must be odd"); int[][] magic = new int[n][n]; int row = n-1; int col = n/2; magic[row][col] = 1; for (int i = 2; i <= n*n; i++) { if (magic[(row + 1) % n][(col + 1) % n] == 0) { row = (row + 1) % n; col = (col + 1) % n; } else { row = (row - 1 + n) % n; // don't change col } magic[row][col] = i; } // print results for (int i = 0; i < n; i++) { for (int j = 0; j < n; j++) { if (magic[i][j] < 10) System.out.print(" "); // for alignment if (magic[i][j] < 100) System.out.print(" "); // for alignment System.out.print(magic[i][j] + " "); } System.out.println(); } } }