回溯算法

八皇后问题（java）：

public class EightRoyal{
  static int[] result = new int[8];
  public static void calresult(int row){
    if(row == 8){
      print_result(result);
      return;
    }
    for(int col = 0; col < 8; col++){
      if(is_ok(row, col))
      {
        result[row] = col;
        calresult(row + 1);
      }
    }
  }

  public static boolean is_ok(int row, int col){
    int left = col - 1;
    int right = col + 1;
    for(int i = row - 1; i >= 0; i--){
      if(result[i] == col){
        return false;
      }
      if(left >= 0){
        if(result[i] == left){
          return false;
        }
      }
      if(right < 8){
        if(result[i] == right){
          return false;
        }
      }
      left--;
      right++;
    }
    return true;
  }

  public static void print_result(int result[]){
    for(int row = 0; row < 8; row++){
      for(int col = 0; col < 8; col++){
        if(result[row] == col){
          System.out.print("Q ");
        }
        else{
          System.out.print("* ");
        }
      }
      System.out.println();
    }
    System.out.println();
  }
  public static void main(String[] argv){
    calresult(0);
  }
}