Given an array of $n$ integers, count the number of subsequences where each element is dictinct.
A subsequence is a sequence of array elements from left to right that may have gaps.
The first line has an integer $n$ : the array size.
The second line has $n$ integers $x_1,x_2,\dots,x_n$ : the array contents.
Print the number of subsequences with distinct elements. The answer can be large, so print it modulo $10^9+7$ .
4 1 2 1 3\n · · · \n
11\n
The subsequences are $[1]$ (two times), $[2]$ , $[3]$ , $[1,2]$ , $[1,3]$ (two times), $[2,1]$ , $[2,3]$ , $[1,2,3]$ and $[2,1,3]$ .