Added Maximum product of 3 numbers in an array #789

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	/**
	* Given an array of numbers, return the maximum product
	* of 3 numbers from the array
	* https://wsvincent.com/javascript-three-sum-highest-product-of-three-numbers/
	* @param {number[]} arrayItems
	* @returns number
	*/
	export function maxProductOfThree(arrayItems) {
	// if size is less than 3, no triplet exists
	let n = arrayItems.length
	if (n < 3) throw new Error('Triplet cannot exist with the given array')
	let max1 = arrayItems[0],
	max2 = -1,
	max3 = -1,
	min1 = arrayItems[0],
	min2 = -1
	for (let i = 1; i < n; i++) {
	if (arrayItems[i] > max1) {
	max3 = max2
	max2 = max1
	max1 = arrayItems[i]
	} else if (max2 === -1 \|\| arrayItems[i] > max2) {
	max3 = max2
	max2 = arrayItems[i]
	} else if (max3 === -1 \|\| arrayItems[i] > max3) {
	max3 = arrayItems[i]
	}
	if (arrayItems[i] < min1) {
	min2 = min1
	min1 = arrayItems[i]
	} else if (min2 === -1 \|\| arrayItems[i] < min2) {
	min2 = arrayItems[i]
	}
	}
	let prod1 = max1 * max2 * max3,
	prod2 = max1 * min1 * min2
	return Math.max(prod1, prod2)
	}

17 changes: 17 additions & 0 deletions Dynamic-Programming/tests/MaxProductOfThree.test.js

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	import { maxProductOfThree } from '../MaxProductOfThree'

	describe('MaxProductOfThree', () => {
	it('expects to throw error for array with only 2 numbers', () => {
	expect(() => {
	maxProductOfThree([1, 3])
	}).toThrow('Triplet cannot exist with the given array')
	})

	it('expects to return 300 as the maximum product', () => {
	expect(maxProductOfThree([10, 6, 5, 3, 1, -10])).toBe(300)
	})

	it('expects to return 300 as the maximum product', () => {
	expect(maxProductOfThree([10, -6, 5, 3, 1, -10])).toBe(600)
	})
	})

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