diff --git a/math/binary_exponent.cpp b/math/binary_exponent.cpp new file mode 100644 index 000000000..b4551da25 --- /dev/null +++ b/math/binary_exponent.cpp @@ -0,0 +1,60 @@ +/// C++ Program to find Binary Exponent Iteratively and Recursively. + +#include +/* + * Calculate a^b in O(log(b)) by converting b to a binary number. + * Binary exponentiation is also known as exponentiation by squaring. + * NOTE : This is a far better approach compared to naive method which provide O(b) operations. + * Example: + * 10 in base 2 is 1010. + * 2^10 = 2^(1010) = 2^8 * 2^2 + * 2^1 = 2 + * 2^2 = (2^1)^2 = 2^2 = 4 + * 2^4 = (2^2)^2 = 4^2 = 16 + * 2^8 = (2^4)^2 = 16^2 = 256 + * Hence to calculate 2^10 we only need to multiply 2^8 and 2^2 skipping 2^1 and 2^4. +*/ + +/// Recursive function to calculate exponent in O(log(n)) using binary exponent. +int binExpo(int a, int b) { + if (b == 0) { + return 1; + } + int res = binExpo(a, b/2); + if (b%2) { + return res*res*a; + } else { + return res*res; + } +} + +/// Iterative function to calculate exponent in O(log(n)) using binary exponent. +int binExpo_alt(int a, int b) { + int res = 1; + while (b > 0) { + if (b%2) { + res = res*a; + } + a = a*a; + b /= 2; + } + return res; +} + +int main() { + int a, b; + /// Give two numbers a, b + std::cin >> a >> b; + if (a == 0 && b == 0) { + std::cout << "Math error" << std::endl; + } else if (b < 0) { + std::cout << "Exponent must be positive !!" << std::endl; + } else { + int resRecurse = binExpo(a, b); + /// int resIterate = binExpo_alt(a, b); + + /// Result of a^b (where '^' denotes exponentiation) + std::cout << resRecurse << std::endl; + /// std::cout << resIterate << std::endl; + } +}