Added Maximum product of 3 numbers in an array

Dynamic-Programming/MaxProductOfThree.js

@@ -0,0 +1,37 @@
+/**
+ *  Given an array of numbers, return the maximum product
+ *  of 3 numbers from the array
+ * @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) return -1
+  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)
+}

Dynamic-Programming/tests/MaxProductOfThree.test.js

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+import { maxProductOfThree } from '../MaxProductOfThree'
+
+describe('MaxProductOfThree', () => {
+  it('expects to return -1 for array with only 2 numbers', () => {
+    expect(maxProductOfThree([1, 3])).toBe(-1)
+  })
+
+  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)
+  })
+})