CareerCup

Not sure I undrstood the qustion correctly...

N = the string
i = postion of the Mask
j = length of N

Mask = N << (j-i)

fn_ReturnMask(int n, int i, int j)
{
int Mask = ConvertToBinary(1*2^i);
return Mask;
}
Test Case:
N=001101
i=2
Mask = 000100
Replace = N XOR Mask (=001001)

mask = (~0<<j)|(~(~0<<i-1));
N = (N&mask)|(M<<i-1);

My understanding of the question =>If M is the string and N is the bits of length 'j' to be replaced in M at 'i' th position then (Assuming the position starts with '0')

ret_mask(int i, int j)
{
mask=0;
if (i>=j)
{
mask=(((1<<j)-1)<<i);
}
return mask;
}

To replace
mask=ret_mask(i,j)
M(M&~mask)|(N<<i);

int mask =0;
int i, j, M,N;

if(i>= j) {

mask =~(~(~0<<j) << i-j) ));

M = (M & mask) | (N << i-j));

}