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Pairs of Equal Values

Easy
You are given an integer array values. Count the index pairs (i, j) with i < j and values[i] == values[j].
Example 1
values=[4, 9, 4, 4, 9] → 4

The three 4s give three pairs and the two 9s give one more, 4 in total.

Example 2
values=[2, 5, 8] → 0

All values differ, so there are no pairs.

Example 3
values=[6] → 0
Constraints
  • 1 ≤ len(values) ≤ 10⁵
  • 1 ≤ values[i] ≤ 100
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Topics
ArrayHash TableMathCounting
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Input
values=[4, 9, 4, 4, 9]
Expected
4

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