Eight queens

51 N-Queens.py

# https://leetcode.com/problems/n-queens/submissions/
class Solution:
    def solveNQueens(self, n: int) -> List[List[str]]:
        queen = [0]*(n+1)
        # print(queen)
        result = []
        def Place(y):
            for x in range(1,y):
                if queen[x] == queen[y] or (abs(queen[x]-queen[y]) == (y-x)):
                    return 0
            return 1
        def Nqueen(y):
            for x in range(1,n+1):
                # print(y,queen)
                queen[y] = x
                if Place(y) and y<=n:
                    if y==n:
                        result.append(Show())
                    else:
                        Nqueen(y+1)
        def Show():
            rlt = []
            print('(',end='')
            for q in queen[1:]:
                print(q,end=',')
                e = ['.']*n
                e[q-1] = 'Q'
                rlt.append(''.join(e))
            print(')\n')
            return rlt
        Nqueen(1)
        return result

generator_iterator.py

# generator_iterator.ipynb
def solve(n):
    solutions = []
    columns = []
    diagonals1 = []
    diagonals2 = []
    def backtrack(row, columns, diagonals1, diagonals2, board):
        if row == n:
            solutions.append(board)
            return
        for col in range(n):
            if col in columns or row+col in diagonals1 or row-col in diagonals2:
                continue
            backtrack(row+1, columns+[col], diagonals1+[row+col], diagonals2+[row-col], board+[col])
    backtrack(0, [], [], [], [])
    return solutions

solutions = solve(8)
for i in solutions:
    for e in i:
        l = [" - "]*8
        l[e] = ' # '
        print(''.join(l))
    print(i)
    print("\n")
print(len(solutions))