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Number Of Boomerangs

A boomerang is a V-shaped sequence that is either upright or upside down.

Specifically, a boomerang can be defined as: sub-array of length 3, with the first and last digits being the same and the middle digit being different.

Some boomerang examples:

[3, 7, 3], [1, -1, 1], [5, 6, 5]

Create a function that returns the total number of boomerangs in an array.

To illustrate:

  • 3 boomerangs in this sequence: [3, 7, 3], [1, 5, 1], [2, -2, 2] 
    [3, 7, 3, 2, 1, 5, 1, 2, 2, -2, 2]

Be aware that boomerangs can overlap, like so:

  • 5 boomerangs (from left to right): [1, 7, 1], [7, 1, 7], [1, 7, 1], [7, 1, 7], and [1, 7, 1] 
    [1, 7, 1, 7, 1, 7, 1]

Examples:

numberOfBoomerangs([9, 5, 9, 5, 1, 1, 1]) ➞ 2
numberOfBoomerangs([5, 6, 6, 7, 6, 3, 9]) ➞ 1
numberOfBoomerangs([4, 4, 4, 9, 9, 9, 9]) ➞ 0

Notes:

  • [5, 5, 5] (triple identical digits) is NOT considered a boomerang because the middle digit is identical to the first and last.

Solution: