Count the number of index pairs whose values differ by exactly k.
Problem
Given an integer array nums and an integer k, count how many index pairs (i, j) satisfy:
i < j|nums[i] - nums[j]| = k
Your task is to return the total number of such pairs.
A pair is counted by index, so two equal values at different positions can contribute multiple pairs.
Input Format
- An integer array
nums - An integer
k
The exact platform input format may vary, but the core task is to count pairs of indices with absolute difference k.
Output Format
Return an integer: the number of index pairs (i, j) such that i < j and |nums[i] - nums[j]| = k.
Constraints
0 <= k- Count pairs by index, not by distinct values.
- If
k = 0, only equal-value pairs contribute. - Use integer arithmetic for counting; the answer may exceed the range of a 32-bit signed integer in some variants.
Example 1
Input
nums = [1, 2, 2, 1], k = 1
Output
4
Explanation
Valid pairs are (1st 1, first 2), (1st 1, second 2), (second 1, first 2), and (second 1, second 2).
Example 2
Input
nums = [1, 3, 5, 8], k = 2
Output
2
Explanation
The valid pairs are (1, 3) and (3, 5).
Show 1 more example
Example 3
Input
nums = [1, 1, 1, 1], k = 0
Output
6
Explanation
Every pair of equal values counts, so the answer is C(4, 2) = 6.
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