algorithm: count the numbers divisible by ‘M’ in a given range (#1185)

* ✅ test cases added for count divisible

* ✨ count divisible math algorithm added

* style fixes

Maths/CountNumbersDivisible.js

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+/**
+ * Count the numbers divisible by ‘M’ in a given range
+ *
+ * @see {@link https://www.tutorialspoint.com/count-the-numbers-divisible-by-m-in-a-given-range-in-cplusplus}
+ *
+ * We have 3 numbers A, B, M as inputs, A and B defines the numbers range [A, B]
+ * Count the total number of divisibles in that range by number M
+ *
+ * @author Chetan07j
+ */
+
+/**
+ * Function to find total divisibles in given range
+ *
+ * @param {number} num1
+ * @param {number} num2
+ * @param {number} divider
+ *
+ * @returns {number} count of total number of divisibles
+ */
+const countNumbersDivisible = (num1, num2, divider) => {
+  if (typeof num1 !== 'number' || typeof num2 !== 'number' || typeof divider !== 'number') {
+    throw new Error('Invalid input, please pass only numbers')
+  }
+
+  // Valid number range is num1 < num2, otherwise throw error
+  if (num1 > num2) {
+    throw new Error('Invalid number range, please provide numbers such that num1 < num2')
+  }
+
+  // if divider is out of range then return 0
+  // as in such case no divisible exists
+  if (divider > num2) {
+    return 0
+  }
+
+  // Find the number of multiples of divider for num1 and num2
+  // integer division part
+  const num1Multiplier = num1 / divider
+  const num2Multiplier = num2 / divider
+
+  // The count of numbers divisibles by divider between num1 and num2
+  let divisibleCount = num2Multiplier - num1Multiplier
+
+  // If num1 is divisible by divider then, edge case for num1 is ignored
+  // which results in 1 less count
+  // to fix that we add +1 in this case
+  if (num1 % divider === 0) {
+    divisibleCount++
+  }
+
+  // As it includes integer division meaning floating values
+  // to get exact count Math.round() is added
+  return Math.round(divisibleCount)
+}
+
+export { countNumbersDivisible }

Maths/test/CountNumbersDivisible.test.js

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+import { countNumbersDivisible } from '../CountNumbersDivisible'
+
+describe('Count the numbers divisible', () => {
+  test.each([
+    [1, 20, 6, 3],
+    [6, 15, 3, 4],
+    [25, 100, 30, 3],
+    [25, 70, 10, 5],
+    [1, 23, 30, 0]
+  ])('Total number(s) divisible between %i to %i by %i is/are %i', (n1, n2, m, expected) => {
+    expect(countNumbersDivisible(n1, n2, m)).toBe(expected)
+  })
+
+  test.each([
+    ['test', 23, 10, 'Invalid input, please pass only numbers'],
+    [44, 30, 10, 'Invalid number range, please provide numbers such that num1 < num2']
+  ])('Should throw an error for input %i, %i, %i, %i', (n1, n2, m, expected) => {
+    expect(() => countNumbersDivisible(n1, n2, m)).toThrowError(expected)
+  })
+})