Merge pull request TheAlgorithms#530 from rahul1995/binary-expo

Add Iterative Binary Exponentiation

Author: ruppysuppy

Maths/BinaryExponentiationIterative.js

@@ -0,0 +1,24 @@
+// To calculate x^n i.e. exponent(x, n) in O(log n) time in iterative way
+// n is an integer and n >= 0
+
+// Explanation: https://en.wikipedia.org/wiki/Exponentiation_by_squaring
+
+// Examples:
+// 2^3 = 8
+// 5^0 = 1
+
+// Uses the fact that
+// exponent(x, n)
+//          = exponent(x*x, floor(n/2))   ; if n is odd
+//          = x*exponent(x*x, floor(n/2)) ; if n is even
+const exponent = (x, n) => {
+  let ans = 1
+  while (n > 0) {
+    if (n % 2 !== 0) ans *= x
+    n = Math.floor(n / 2)
+    if (n > 0) x *= x
+  }
+  return ans
+}
+
+export { exponent }

Maths/test/BinaryExponentiationIterative.test.js

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+import { exponent } from '../BinaryExponentiationIterative'
+
+describe('exponent', () => {
+  it('should return 1 when power is 0', () => {
+    expect(exponent(5, 0)).toBe(1)
+  })
+
+  it('should return 0 when base is 0', () => {
+    expect(exponent(0, 7)).toBe(0)
+  })
+
+  it('should return the value of a base raised to a power', () => {
+    expect(exponent(3, 5)).toBe(243)
+  })
+})