How should I practice Count Equal-Offset Pairs Within an Index Distance?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Google phone screen problems in FastPrep.

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Count Equal-Offset Pairs Within an Index Distance

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Problem statement

Given an integer array nums and an integer k, count index pairs (i,j) satisfying 0 <= i < j < nums.length, j - i < k, and nums[i] - nums[j] = i - j.

Return the exact count as a signed 64-bit integer. When k <= 1, no pair qualifies.

Function

countEqualOffsetPairs(nums: int[], k: int) → long

Examples

Example 1

nums = [3,4,5,7]k = 4return = 3

The transformed values nums[i]-i are [3,3,3,4]; the first three indices form three qualifying pairs.

Example 2

nums = [1,2,3,4]k = 2return = 3

Only adjacent pairs are within strict distance two, and all share the same transformed value.

Example 3

nums = [5,5,5]k = 5return = 0

The transformed values are distinct, so no pair satisfies the equality.

Constraints

0 <= nums.length <= 200000.
-10^9 <= nums[i] <= 10^9.
0 <= k <= 10^9.