Assignment-4.py

# Number of queens
n=4
# Matrix
a=[[0,0,0,0],[0,0,0,0],[0,0,0,0],[0,0,0,0]]
# Dictionary for backtrack
b={}

# Checking if column is safe
def isColumnSafe(r,c):
    while(r>=0):
        if(a[r][c] == 1):
            return 0
        r = r-1
    return 1

# Checking if left diagonal is safe
def isLeftDiagonalSafe(r,c):
    while(r>=0 and c>=0):
        if(a[r][c] == 1):
            return 0
        r = r-1
        c = c-1
    return 1

# Checking if right diagonal is safe
def isRightDiagonalSafe(r,c):
    while(r>=0 and c<n):
        if(a[r][c]==1):
            return 0
        r = r-1
        c = c+1
    return 1

def isSafe(r,c):
    if(isColumnSafe(r,c) and isLeftDiagonalSafe(r,c) and isRightDiagonalSafe(r,c)):
        return True
    return False
def chessboard(r,c):
    if(r>=n):
        return 
    p = 0
    while c<n:
        p = isSafe(r,c)
        if p == 1:
            a[r][c] = 1
            b.update({r:c})
            break
        c=c+1
    
    if p==1:
        chessboard(r+1,0)
    else:
        a[r-1][b.get(r-1)]=0
        chessboard(r-1,int(b.get(r-1))+1)
chessboard(0,0)
print("Matrix is:- ",a)
print("Dictionary is:- ",b)