64 lines
2.0 KiB
Java
64 lines
2.0 KiB
Java
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NQueens Problem
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class nQueens {
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static int N = 8;
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static int numSolutions = 0;
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static boolean safe(int row, int column, int[] board) {
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// Check whether it is safe to place a queen at row, column;
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// i.e., is board[column]=row a safe configuration?
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for (int j=1; j if (board[column-j] == row ||
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board[column-j] == row-j ||
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board[column-j] == row+j) {
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return false;
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}
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}
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return true;
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}
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static void place(int column, int[] board) {
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// Place a queen in all safe positions of column c,
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// then try placing a queen in the next column.
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// If a position in column N is safe, print the board.
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for (int row = 1; row <= N; row++) {
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board[column] = row;
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if (safe(row, column, board)) {
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if (column==N) numSolutions++; // we have a solution
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else place(column+1, board); // try next column
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}
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board[column] = 0; // unrecord that a queen was placed
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}
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}
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public static void main(String[] args) {
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System.out.println("nQueens loaded");
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try { // override default from command line argument if any
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N = Integer.parseInt(args[0]);
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} catch (ArrayIndexOutOfBoundsException e) {
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} catch (NumberFormatException e) {
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}
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System.out.println("nQueens: N=" + N);
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int[] board = new int[N+1]; // N+1 since we need board[1]...board[N]
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place(1, board);
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System.out.println("nQueens: numSolutions=" + numSolutions);
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System.out.println("nQueens done");
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}
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}
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/* ............... Example compile and run(s)
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D:\>javac nque.java
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D:\>java nQueens
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nQueens loaded
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nQueens: N=8
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nQueens: numSolutions=92
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nQueens done
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D:\>java nQueens 10
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nQueens loaded
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nQueens: N=10
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nQueens: numSolutions=724
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nQueens done
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... end of example run(s) */
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