Question

The minimum number in a subarray of size L. I have to find it for all the subarrays of the array. Is there any other way than scanning through all the subarrays individually?

I have one solution in mind:

a[n]//the array
minimum[n-l+1]//the array to store the minimum numbers

minpos=position_minimum_in_subarray(a,0,l-1);
minimum[0]=a[minpos];
for(i=1;i<=n-l-1;i++)
{
    if(minpos=i-1)
    {
        minpos=position_minimum_in_subarray(a,i,i+l-1);
    }
    else {
        if(a[minpos]>a[i+l-1]) minpos=i+l-1;
        minimum=a[minpos];
    }
}

Is there any better solution than this?

Answer 1

You can use a double ended queue(Q) .Find a way such that the smallest element always appears at the front of the Q and the size of Q never exceeds L. Thus you are always inserting and deleting elements at most once making the solution O(n). I feel this is enough hint to get you going.