八皇后问题

import java.util.*;/** * 八皇后问题 * @author oracs * @date 2008-06-04 */public class EightQueens {    private static final int N = 8;    private int[] queen = new int[N];    private int count = 0;    // constructor    public EightQueens() {        for (int i = 0; i < N; i++) {            queen[i] = -1;        }    }        /**     * @param args     */    public static void main(String[] args) {        EightQueens q = new EightQueens();        q.findQueen(0);    }        public boolean isQueenAtChest(int i, int j) {        boolean result = false;                if (j == 0) {  // init queen array            queen[0] = i;            return true;        }        else {            // loop queen array, find whether the next queen is in the right positon            for (int queen_col = 0; queen_col < queen.length; queen_col++) {                int queen_row = queen[queen_col];                if ( queen_row != -1) {                    if ( (i == queen_row) // 同一横线                       ||((i >= queen_row) && (i == j + (queen_row - queen_col))) // 主对角线                       ||((i < queen_row) && (i ==  (queen_row + queen_col) - j))) { // 斜对角线                                                return false;                    }                }                                if (queen_col == queen.length - 1) {                    queen[j] = i;                    return true;                }            }        }                return result;    }        public void findQueen(int col) {        if (col < N) {            // loop every row in col            for (int row = 0; row < N; row++) {                if (isQueenAtChest(row, col)) {                    // recursion                    findQueen(col+1);                }            }                        // print the queen            if (col == N - 1) {                printQueen();            }                        // clear queen            clearQueen(col);        }    }        // print queen    public void printQueen() {        for (int i = 0; i < queen.length; i++) {            if (queen[i] == -1) return;        }                System.out.println(++count +":" + Arrays.toString(queen));    }        // initial -1 to queen 's back position    public void clearQueen(int col) {        for (int i = col; i < N; i++) {            queen[i] = -1;        }    }}