Code not working

#1

code- https://ide.codingblocks.com/s/331350
It works for the test case given in the exmaple

#2 
    ll mx=0,mn=0;

    sort(a,a+n);

    for(int i=0;i<n/2;i++)

    {

        mx+=(a[i+n/2]-a[i]);

        mn+=(a[2*i+1]-a[2*i]);

    }

here is the simple approach to it

#3

in the for loop condition what does i&it mean?

#4

I is index or iterator