Eight Queens Problem

A horse wants to travel across the chessboard

సీతారామకళ్యాణం sita rama kalyanam

చంటబ్బాయి chantabbayi

तेजाब - Tejab

Merging point of two linked lists

Problem Statement:
You need to find all possible solutions to place eight queens on a chess board - Condition is no two queens should be able to collide.
Note: Queen can move diagonally or linearly to any length.
string answer = "";
int q1 = 0;
int q2 = 0;
int q3 = 0;
int q4 = 0;
int q5 = 0;
int q6 = 0;
int q7 = 0;
int q8 = 0;

int counter = 0;

for ( q1 = 1; q1 < 9; q1++)
{
for ( q2 = 1; q2 < 9; q2++)
{
if ((q1 != q2)&& ( Math.Abs(q1 - q2) != 1 ) )
{
for ( q3 = 1; q3 < 9; q3++)
{
if ((q1 != q3) && (q2 != q3) && (Math.Abs(q1 - q3) != 2) && (Math.Abs(q2 - q3) != 1))
{
for ( q4 = 1; q4 < 9; q4++)
{
if ((q1 != q4) && (q2 != q4) && (q3 != q4) && (Math.Abs(q1 - q4) != 3) && (Math.Abs(q2 - q4) != 2) && (Math.Abs(q3 - q4) != 1))
{
for ( q5 = 1; q5 < 9; q5++)
{
if ((q1 != q5) && (q2 != q5) && (q3 != q5) && (q4 != q5) && (Math.Abs(q1 - q5) != 4) && (Math.Abs(q2 - q5) != 3) && (Math.Abs(q3 - q5) != 2) && (Math.Abs(q4 - q5) != 1))
{
for ( q6 = 1; q6 < 9; q6++)
{
if ((q1 != q6) && (q2 != q6) && (q3 != q6) && (q4 != q6) && (q5 != q6)
&& (Math.Abs(q1 - q6) != 5)
&& (Math.Abs(q2 - q6) != 4)
&& (Math.Abs(q3 - q6) != 3)
&& (Math.Abs(q4 - q6) != 2)
&& (Math.Abs(q5 - q6) != 1))
{
for ( q7 = 1; q7 < 9; q7++)
{
if ((q1 != q7) && (q2 != q7) && (q3 != q7) && (q4 != q7) && (q5 != q7) && (q6 != q7)
&& (Math.Abs(q1 - q7) != 6)
&& (Math.Abs(q2 - q7) != 5)
&& (Math.Abs(q3 - q7) != 4)
&& (Math.Abs(q4 - q7) != 3)
&& (Math.Abs(q5 - q7) != 2)
&& (Math.Abs(q6 - q7) != 1))
{
for ( q8 = 1; q8 < 9; q8++)
{
if ((q1 != q8) && (q2 != q8) && (q3 != q8) && (q4 != q8) && (q5 != q8) && (q6 != q8) && (q7 != q8)
&& (Math.Abs(q1 - q8) != 7)
&& (Math.Abs(q2 - q8) != 6)
&& (Math.Abs(q3 - q8) != 5)
&& (Math.Abs(q4 - q8) != 4)
&& (Math.Abs(q5 - q8) != 3)
&& (Math.Abs(q6 - q8) != 2)
&& (Math.Abs(q7 - q8) != 1))
{
counter++;
answer += counter.ToString() + ": " +
"(1," + q1.ToString() + "),"+
"(2," + q2.ToString() + ")," +
"(3," + q3.ToString() + ")," +
"(4," + q4.ToString() + ")," +
"(5," + q5.ToString() + ")," +
"(6," + q6.ToString() + ")," +
"(7," + q7.ToString() + ")," +
"(8," + q8.ToString() + ")" + "\n\r";
}
}
}
}
}
}
}
}
}
}
}
}

}
}


}
MessageBox.Show(answer );
label2.Text = answer;
Messagebox output:
1: (1,1),(2,5),(3,8),(4,6),(5,3),(6,7),(7,2),(8,4)

2: (1,1),(2,6),(3,8),(4,3),(5,7),(6,4),(7,2),(8,5)

3: (1,1),(2,7),(3,4),(4,6),(5,8),(6,2),(7,5),(8,3)

4: (1,1),(2,7),(3,5),(4,8),(5,2),(6,4),(7,6),(8,3)

5: (1,2),(2,4),(3,6),(4,8),(5,3),(6,1),(7,7),(8,5)

6: (1,2),(2,5),(3,7),(4,1),(5,3),(6,8),(7,6),(8,4)

7: (1,2),(2,5),(3,7),(4,4),(5,1),(6,8),(7,6),(8,3)

8: (1,2),(2,6),(3,1),(4,7),(5,4),(6,8),(7,3),(8,5)

9: (1,2),(2,6),(3,8),(4,3),(5,1),(6,4),(7,7),(8,5)

10: (1,2),(2,7),(3,3),(4,6),(5,8),(6,5),(7,1),(8,4)

11: (1,2),(2,7),(3,5),(4,8),(5,1),(6,4),(7,6),(8,3)

12: (1,2),(2,8),(3,6),(4,1),(5,3),(6,5),(7,7),(8,4)

13: (1,3),(2,1),(3,7),(4,5),(5,8),(6,2),(7,4),(8,6)

14: (1,3),(2,5),(3,2),(4,8),(5,1),(6,7),(7,4),(8,6)

15: (1,3),(2,5),(3,2),(4,8),(5,6),(6,4),(7,7),(8,1)

16: (1,3),(2,5),(3,7),(4,1),(5,4),(6,2),(7,8),(8,6)

17: (1,3),(2,5),(3,8),(4,4),(5,1),(6,7),(7,2),(8,6)

18: (1,3),(2,6),(3,2),(4,5),(5,8),(6,1),(7,7),(8,4)

19: (1,3),(2,6),(3,2),(4,7),(5,1),(6,4),(7,8),(8,5)

20: (1,3),(2,6),(3,2),(4,7),(5,5),(6,1),(7,8),(8,4)

21: (1,3),(2,6),(3,4),(4,1),(5,8),(6,5),(7,7),(8,2)

22: (1,3),(2,6),(3,4),(4,2),(5,8),(6,5),(7,7),(8,1)

23: (1,3),(2,6),(3,8),(4,1),(5,4),(6,7),(7,5),(8,2)

24: (1,3),(2,6),(3,8),(4,1),(5,5),(6,7),(7,2),(8,4)

25: (1,3),(2,6),(3,8),(4,2),(5,4),(6,1),(7,7),(8,5)

26: (1,3),(2,7),(3,2),(4,8),(5,5),(6,1),(7,4),(8,6)

27: (1,3),(2,7),(3,2),(4,8),(5,6),(6,4),(7,1),(8,5)

28: (1,3),(2,8),(3,4),(4,7),(5,1),(6,6),(7,2),(8,5)

29: (1,4),(2,1),(3,5),(4,8),(5,2),(6,7),(7,3),(8,6)

30: (1,4),(2,1),(3,5),(4,8),(5,6),(6,3),(7,7),(8,2)

31: (1,4),(2,2),(3,5),(4,8),(5,6),(6,1),(7,3),(8,7)

32: (1,4),(2,2),(3,7),(4,3),(5,6),(6,8),(7,1),(8,5)

33: (1,4),(2,2),(3,7),(4,3),(5,6),(6,8),(7,5),(8,1)

34: (1,4),(2,2),(3,7),(4,5),(5,1),(6,8),(7,6),(8,3)

35: (1,4),(2,2),(3,8),(4,5),(5,7),(6,1),(7,3),(8,6)

36: (1,4),(2,2),(3,8),(4,6),(5,1),(6,3),(7,5),(8,7)

37: (1,4),(2,6),(3,1),(4,5),(5,2),(6,8),(7,3),(8,7)

38: (1,4),(2,6),(3,8),(4,2),(5,7),(6,1),(7,3),(8,5)

39: (1,4),(2,6),(3,8),(4,3),(5,1),(6,7),(7,5),(8,2)

40: (1,4),(2,7),(3,1),(4,8),(5,5),(6,2),(7,6),(8,3)

41: (1,4),(2,7),(3,3),(4,8),(5,2),(6,5),(7,1),(8,6)

42: (1,4),(2,7),(3,5),(4,2),(5,6),(6,1),(7,3),(8,8)

43: (1,4),(2,7),(3,5),(4,3),(5,1),(6,6),(7,8),(8,2)

44: (1,4),(2,8),(3,1),(4,3),(5,6),(6,2),(7,7),(8,5)

45: (1,4),(2,8),(3,1),(4,5),(5,7),(6,2),(7,6),(8,3)

46: (1,4),(2,8),(3,5),(4,3),(5,1),(6,7),(7,2),(8,6)

47: (1,5),(2,1),(3,4),(4,6),(5,8),(6,2),(7,7),(8,3)

48: (1,5),(2,1),(3,8),(4,4),(5,2),(6,7),(7,3),(8,6)

49: (1,5),(2,1),(3,8),(4,6),(5,3),(6,7),(7,2),(8,4)

50: (1,5),(2,2),(3,4),(4,6),(5,8),(6,3),(7,1),(8,7)

51: (1,5),(2,2),(3,4),(4,7),(5,3),(6,8),(7,6),(8,1)

52: (1,5),(2,2),(3,6),(4,1),(5,7),(6,4),(7,8),(8,3)

53: (1,5),(2,2),(3,8),(4,1),(5,4),(6,7),(7,3),(8,6)

54: (1,5),(2,3),(3,1),(4,6),(5,8),(6,2),(7,4),(8,7)

55: (1,5),(2,3),(3,1),(4,7),(5,2),(6,8),(7,6),(8,4)

56: (1,5),(2,3),(3,8),(4,4),(5,7),(6,1),(7,6),(8,2)

57: (1,5),(2,7),(3,1),(4,3),(5,8),(6,6),(7,4),(8,2)

58: (1,5),(2,7),(3,1),(4,4),(5,2),(6,8),(7,6),(8,3)

59: (1,5),(2,7),(3,2),(4,4),(5,8),(6,1),(7,3),(8,6)

60: (1,5),(2,7),(3,2),(4,6),(5,3),(6,1),(7,4),(8,8)

61: (1,5),(2,7),(3,2),(4,6),(5,3),(6,1),(7,8),(8,4)

62: (1,5),(2,7),(3,4),(4,1),(5,3),(6,8),(7,6),(8,2)

63: (1,5),(2,8),(3,4),(4,1),(5,3),(6,6),(7,2),(8,7)

64: (1,5),(2,8),(3,4),(4,1),(5,7),(6,2),(7,6),(8,3)

65: (1,6),(2,1),(3,5),(4,2),(5,8),(6,3),(7,7),(8,4)

66: (1,6),(2,2),(3,7),(4,1),(5,3),(6,5),(7,8),(8,4)

67: (1,6),(2,2),(3,7),(4,1),(5,4),(6,8),(7,5),(8,3)

68: (1,6),(2,3),(3,1),(4,7),(5,5),(6,8),(7,2),(8,4)

69: (1,6),(2,3),(3,1),(4,8),(5,4),(6,2),(7,7),(8,5)

70: (1,6),(2,3),(3,1),(4,8),(5,5),(6,2),(7,4),(8,7)

71: (1,6),(2,3),(3,5),(4,7),(5,1),(6,4),(7,2),(8,8)

72: (1,6),(2,3),(3,5),(4,8),(5,1),(6,4),(7,2),(8,7)

73: (1,6),(2,3),(3,7),(4,2),(5,4),(6,8),(7,1),(8,5)

74: (1,6),(2,3),(3,7),(4,2),(5,8),(6,5),(7,1),(8,4)

75: (1,6),(2,3),(3,7),(4,4),(5,1),(6,8),(7,2),(8,5)

76: (1,6),(2,4),(3,1),(4,5),(5,8),(6,2),(7,7),(8,3)

77: (1,6),(2,4),(3,2),(4,8),(5,5),(6,7),(7,1),(8,3)

78: (1,6),(2,4),(3,7),(4,1),(5,3),(6,5),(7,2),(8,8)

79: (1,6),(2,4),(3,7),(4,1),(5,8),(6,2),(7,5),(8,3)

80: (1,6),(2,8),(3,2),(4,4),(5,1),(6,7),(7,5),(8,3)

81: (1,7),(2,1),(3,3),(4,8),(5,6),(6,4),(7,2),(8,5)

82: (1,7),(2,2),(3,4),(4,1),(5,8),(6,5),(7,3),(8,6)

83: (1,7),(2,2),(3,6),(4,3),(5,1),(6,4),(7,8),(8,5)

84: (1,7),(2,3),(3,1),(4,6),(5,8),(6,5),(7,2),(8,4)

85: (1,7),(2,3),(3,8),(4,2),(5,5),(6,1),(7,6),(8,4)

86: (1,7),(2,4),(3,2),(4,5),(5,8),(6,1),(7,3),(8,6)

87: (1,7),(2,4),(3,2),(4,8),(5,6),(6,1),(7,3),(8,5)

88: (1,7),(2,5),(3,3),(4,1),(5,6),(6,8),(7,2),(8,4)

89: (1,8),(2,2),(3,4),(4,1),(5,7),(6,5),(7,3),(8,6)

90: (1,8),(2,2),(3,5),(4,3),(5,1),(6,7),(7,4),(8,6)

91: (1,8),(2,3),(3,1),(4,6),(5,2),(6,5),(7,7),(8,4)

92: (1,8),(2,4),(3,1),(4,3),(5,6),(6,2),(7,7),(8,5)

Here are details of problem .

1) imagine rows 1,2,3,4,5,6,7,8

2) Now you want to place queens on 8 rows one in each row( one queeen per row :part of queens scope)

3) so each can be placed in any of 8 columns of each row.

4) when you place each one check it is not hitting any previously positioned queen.

5) Rest try to understand the code.


improve:
Int can be replaced with tiny int. (one byte can represent 8 possibilities)
This is a processor intesive and memory conservative algorithm.

Bad: hardcoded 8 alla across.

N queens on NXN square will be good problem to solve.