Solve Eight Queens problem with 1D array

The following program prints out all solutions for N Queens problem. 

There are 92 solutions for 8 Queens.

 The solution uses a 1D array and does not use recursion.

 public class EightQueen {  
   
      private static final int N = 8;  
      //queens[2]=3, means the queen on row 2 is placed on column 3
      private static int[] queens = new int[N];  
      private static int index = 0;  
      private static int counter = 0;  
        
      public static void placeQueens(){  
           int previousColumn = -1;  
           boolean noMoreSolutions = false;  
           while (!noMoreSolutions){  
                while (index < N){  
                     int col = getColumnForNextRow(previousColumn);  
                     if (col != -1){  
                          queens[index++] = col;  
                          previousColumn = -1;  
                     }else if (index > 0){  
                          previousColumn = queens[--index];  
                     }else{  
                          noMoreSolutions = true;  
                          System.out.println("No More Solutions");  
                          break;  
                     }  
                }  
                if (!noMoreSolutions){  
                     print();  
                     System.out.println("Solution #"+ ++counter);  
                     //Let's find another solution  
                     previousColumn = queens[--index];  
                }  
           }  
      }  
        
      private static int getColumnForNextRow(int previousColumn) {  
           int startCol = previousColumn + 1;  
           for (int j=startCol; j < N; j++){  
                if (!canAttackExistingQueens(j)){  
                     return j;  
                }  
           }  
           return -1;  
      }  
        
      private static boolean canAttackExistingQueens(int col) {  
           for (int i=0; i<index; i++){  
                if (canAttackQueen(index, col, i, queens[i])){  
                     return true;  
                }  
           }  
           return false;  
      }  
   
      private static boolean canAttackQueen(int row1, int col1, int row2, int col2) {  
           return sameCol(col1, col2) || sameDiagonal(row1, col1, row2, col2);  
      }  
   
      private static boolean sameCol(int col1, int col2) {  
           return col1 == col2;  
      }  
   
      private static boolean sameDiagonal(int row1, int col1, int row2, int col2) {  
           return col1 - col2 == row1 - row2 || col1 - col2 == row2 - row1;  
      }  
        
      private static void print(){  
           for (int i=0; i<N; i++){  
                for (int j=0; j<N; j++){  
                     if (queens[i] == j){  
                          System.out.print("Q ");  
                     }else{  
                          System.out.print("* ");  
                     }  
                }  
                System.out.println();  
           }       
      }  
   
      /**  
       * @param args  
       */  
      public static void main(String[] args) {  
           placeQueens();  
      }  
 }