Link to the DSERIES Problem: DSERIES Problem
Link to the DSeries editoral: DSERIES EDITORIAL
Link to the Author’s Solution: Author’s solution
I didn’t understand that why did the author used:
temp =(temp- fact[ t+1 ] + M )%M ;
and where or how did he divide the temp by t+1.
what is this line used for?
temp = ( temp * powd( t + 1 , M -2 , M ) )%M ;
@abhi_1595 @aswinashok44 Please help me out!!!
If anyone is having problem in understanding the code then head over to the above link…
As you must have seen in editorial, the ans is (product of (n+i) where i ranges from 1 to t+1/(t+1))-t! but
this is equal to [(product of (n+i) where i ranges from 1 to t+1)-(t+1)!]/(t+1) (multiplying t! by t+1 up and down like 2/3 +1 =(2+3)/3) this gives the explanation of first line
second line is about dividing the whole by t+1, as we have to do mod m we have to use modular division. But author has used Fermat’s little theorem details about which is given here
and proof here in this ans https://stackoverflow.com/questions/12235110/modulo-of-division-oftwo-numbers/12235283#12235283
By this we get (a/b)%m = (a*b^m-2)%m so that’s what author has done
Hope this helps!!