A14174. Same Differences

You are given an array $a$ of $n$ integers. Count the number of pairs of indices $(i, j)$ such that $i < j$ and $a_j - a_i = j - i$ .

The first line contains one integer $t$ ( $1 \le t \le 10^4$ ). Then $t$ test cases follow.

The first line of each test case contains one integer $n$ ( $1 \le n \le 2 \cdot 10^5$ ).

The second line of each test case contains $n$ integers $a_1, a_2, \ldots, a_n$ ( $1 \le a_i \le n$ ) — array $a$ .

It is guaranteed that the sum of $n$ over all test cases does not exceed $2 \cdot 10^5$ .

For each test case output the number of pairs of indices $(i, j)$ such that $i < j$ and $a_j - a_i = j - i$ .