Given an integer array nums and an integer k, return the number of index pairs (i, j) such that i $<$ j and the absolute difference between nums[i] and nums[j] equals k.

Constraints:

• $1 \leq$ nums.length $\leq 200$

• $1 \leq$ nums[i] $\leq 100$

• $1 \leq$ k $\leq 99$

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