------------------------------BSF------------------------------
from collections import defaultdict


graph = defaultdict(list)

def addEdge(u,v):
    graph[u].append(v)
    graph[v].append(u)

def BFS(source):
    open = []
    closed = []
    open.append(source)
    while len(open) > 0:
        node = open[0]
        print(node,sep=" ")
        closed.append(node)
        open.pop(0)
        # print(top)
        neighbours = graph[node]

        for neighbour in neighbours:
            if neighbour not in open and neighbour not in closed:
                # open = open.append(neighbour)
                open = open + [neighbour]


addEdge(1,2)
addEdge(1,3)
addEdge(2,4)
addEdge(2,5)
addEdge(3,6)
addEdge(3,7)
BFS(1)

--------------------------------n QUEENS--------------------

def isSafe(board,row,col):
    for i in range(col):
        if board[row][i] == 1:
            return False

    for i,j in zip(range(row,-1,-1),range(col,-1,-1)):
        if board[i][j] == 1:
            return False


    for i,j in zip(range(row,N),range(col,-1,-1)):
        if board[i][j] == 1:
            return False

    return True

def solve(board,col):
    if col >= N:
        return True

    for row in range(N):
        if isSafe(board,row,col):
            board[row][col] = 1

            if solve(board,col+1):
                return True

            board[row][col] = 0

    return False

N = 3
board = [[0 for _ in range(N)] for _ in range(N)]
if solve(board,0):
    for row in board:
        print(row)
else:
    print("Cant place "+ str(N) + " queens on NxN matrix")