Good Subsequence
Practice
4.5 (2 votes)
Math
Observation
Basic math
C++
Problem
22% Success 417 Attempts 20 Points 1s Time Limit 256MB Memory 1024 KB Max Code

You are given an array A of length N. A subsequence is called good if all the elements of that subsequence are distinct. Find the number of non-empty good subsequences modulo 109+7.

Two subsequences are different if they differ in the indices chosen.

Input Format:

  • The first line contains an integer T, which denotes the number of test cases.
  • The first line of each test case contains an integer N.
  • The second line of each test case contains N space-separated integers, elements of array A.

Output Format:

For each test case, print the number of non-empty good subsequences modulo 109+7.

Constraints:

1≤T≤10
1≤N≤105
1≤A[i]≤105

Sample Input
2
3
2 3 1 
4
1 1 1 1
Sample Output
7
4
Explanation

First test case:
Good subsequences are [2],[3],[1],[2,3],[2,1],[3,1],[2,3,1]. Hence, the answer is 7.

Second test case:
Good subsequences are [1],[1],[1],[1]. Hence, the answer is 4.

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