A15214 | $Yet Another Problem About Pairs Satisfying an Inequality$

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题目描述

You are given an array $a_1, a_2, \dots a_n$ . Count the number of pairs of indices $1 \leq i, j \leq n$ such that $a_i < i < a_j < j$ .

The first line contains an integer $t$ ( $1 \leq t \leq 1000$ ) — the number of test cases. The first line of each test case contains an integer $n$ ( $2 \leq n \leq 2 \cdot 10^5$ ) — the length of the array. The second line of each test case contains $n$ integers $a_1, a_2, \dots, a_n$ ( $0 \leq a_i \leq 10^9$ ) — the elements of the array. It is guaranteed that the sum of $n$ across all test cases does not exceed $2 \cdot 10^5$ .

For each test case, output a single integer — the number of pairs of indices satisfying the condition in the statement. Please note, that the answer for some test cases won't fit into 32-bit integer type, so you should use at least 64-bit integer type in your programming language (like long long for C++).

输入 #1

5
8
1 1 2 3 8 2 1 4
2
1 2
10
0 2 1 6 3 4 1 2 8 3
2
1 1000000000
3
0 1000000000 2

输出 #1

C++ 编辑器

输入

输出