Evenly Spaced Triples

Easy

You are given a strictly increasing array values and a positive integer step. A triple of indices i < j < k is good if values[j] - values[i] == step and values[k] - values[j] == step. Return the number of good triples.

Example 1

values=[2, 5, 8, 9, 11, 14], step=3 → 3

The triples 2, 5, 8 / 5, 8, 11 / 8, 11, 14 all work.

Example 2

values=[0, 1, 3, 4, 7], step=2 → 0

Each step must be 2: 1 → 3 exists but 5 does not, and 0 → 2 fails since there is no 2. The answer is 0.

Example 3

values=[10, 20, 30, 40], step=10 → 2

Constraints

3 ≤ len(values) ≤ 200
0 ≤ values[i] ≤ 200
1 ≤ step ≤ 50
values is strictly increasing

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Topics

Array Hash Table Two Pointers Enumeration

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Input

values=[2, 5, 8, 9, 11, 14], step=3

Expected

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