You are given a?0-indexed?integer array?nums. A pair of indices?(i, j)?is a?bad pair?if?i < j?and?j - i != nums[j] - nums[i].

Return?the total number of?bad pairs?in?nums.

?

Example 1:

Input: nums = [4,1,3,3]

Output: 5

Explanation:?

The pair (0, 1) is a bad pair since 1 - 0 != 1 - 4.?

The pair (0, 2) is a bad pair since 2 - 0 != 3 - 4, 2 != -1.?

The pair (0, 3) is a bad pair since 3 - 0 != 3 - 4, 3 != -1.?

The pair (1, 2) is a bad pair since 2 - 1 != 3 - 1, 1 != 2.?

The pair (2, 3) is a bad pair since 3 - 2 != 3 - 3, 1 != 0.?

There are a total of 5 bad pairs, so we return 5.

Example 2:

Input: nums = [1,2,3,4,5]

Output: 0

Explanation: There are no bad pairs.

?

Constraints:

• 1 <= nums.length <= 105

• 1 <= nums[i] <= 109

• 考慮good pair，也就是i-nums[i]的數(shù)量，然后利用一點點數(shù)學排列組合的知識即可。

Runtime:?50 ms, faster than?34.50%?of?Java?online submissions for?Count Number of Bad Pairs.

Memory Usage:?53.9 MB, less than?89.52%?of?Java?online submissions for?Count Number of Bad Pairs.