# N-queens problem

``````func N_queens_solution(N = 8) {

func collision(field, row) {
for i in (^row) {
var distance = (field[i] - field[row])
distance ~~ [0, row-i, i-row] && return true
}
return false
}

func search(field, row) {
row == N && return field
for i in (^N) {
field[row] = i
if (!collision(field, row)) {
return (__FUNC__(field, row+1) || next)
}
}
return []
}

for i in (0 .. N>>1) {
if (var r = search([i], 1)) {
return r
}
}
}

for n in (1..15) {
say "#{'%2d' % n}: #{N_queens_solution(n) || 'No solution'}"
}
``````

#### Output:

`````` 1: [0]
2: No solution
3: No solution
4: [1, 3, 0, 2]
5: [0, 2, 4, 1, 3]
6: [1, 3, 5, 0, 2, 4]
7: [0, 2, 4, 6, 1, 3, 5]
8: [0, 4, 7, 5, 2, 6, 1, 3]
9: [0, 2, 5, 7, 1, 3, 8, 6, 4]
10: [0, 2, 5, 7, 9, 4, 8, 1, 3, 6]
11: [0, 2, 4, 6, 8, 10, 1, 3, 5, 7, 9]
12: [0, 2, 4, 7, 9, 11, 5, 10, 1, 6, 8, 3]
13: [0, 2, 4, 1, 8, 11, 9, 12, 3, 5, 7, 10, 6]
14: [0, 2, 4, 6, 11, 9, 12, 3, 13, 8, 1, 5, 7, 10]
15: [0, 2, 4, 1, 9, 11, 13, 3, 12, 8, 5, 14, 6, 10, 7]
``````