Add Iterative Binary Exponentiation

rahul1995 · rahul1995 · commit ae3bd72ca843 · 2020-10-29T21:36:31.000+05:30
diff --git a/Maths/BinaryExponentiationIterative.js b/Maths/BinaryExponentiationIterative.js
@@ -0,0 +1,22 @@
+// To calculate x^n i.e. exponent(x, n) in O(log n) time in iterative way
+// n is an integer and n >= 0
+
+// 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 }
diff --git a/Maths/test/BinaryExponentiationIterative.test.js b/Maths/test/BinaryExponentiationIterative.test.js
@@ -0,0 +1,15 @@
+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)
+    })
+})
