From 6272b2af084953471348442c79e19a6030c18427 Mon Sep 17 00:00:00 2001 From: Prashant Thakur Date: Sun, 17 Oct 2021 06:27:23 +0530 Subject: [PATCH] feat: Modified count_set_bits.cpp (#1634) * Modified: Replaced existing code with faster implementation * Changed long long to "int64_t" * Indentation Fixed. * Modified Documentation. * Updated authors of count_set_bits.cpp Co-authored-by: David Leal * Apply suggestions from code review Co-authored-by: David Leal * Added proper indentation in "main" function Co-authored-by: David Leal Co-authored-by: David Leal --- bit_manipulation/count_of_set_bits.cpp | 51 +++++++++++++------------- 1 file changed, 26 insertions(+), 25 deletions(-) diff --git a/bit_manipulation/count_of_set_bits.cpp b/bit_manipulation/count_of_set_bits.cpp index 87f01d161..497346a53 100644 --- a/bit_manipulation/count_of_set_bits.cpp +++ b/bit_manipulation/count_of_set_bits.cpp @@ -1,26 +1,21 @@ /** * @file - * @brief Implementation to [count sets - * bits](https://www.geeksforgeeks.org/count-set-bits-in-an-integer/) in an + * @brief Implementation to [count number of set bits of a number] + * (https://www.geeksforgeeks.org/count-set-bits-in-an-integer/) in an * integer. * * @details - * We are given an integer number. Let’s say, number. The task is to first - * calculate the binary digit of a number and then calculate the total set bits - * of a number. + * We are given an integer number. We need to calculate the number of set bits in it. * - * Set bits in a binary number is represented by 1. Whenever we calculate the - * binary number of an integer value it is formed as the combination of 0’s and - * 1’s. So digit 1 is known as a set bit in computer terms. - * Time Complexity: O(log n) + * A binary number consists of two digits. They are 0 & 1. Digit 1 is known as + * set bit in computer terms. + * Worst Case Time Complexity: O(log n) * Space complexity: O(1) * @author [Swastika Gupta](https://github.com/Swastyy) + * @author [Prashant Thakur](https://github.com/prashant-th18) */ - #include /// for assert -#include /// for io operations -#include /// for std::vector - +#include /// for IO operations /** * @namespace bit_manipulation * @brief Bit manipulation algorithms @@ -36,24 +31,27 @@ namespace count_of_set_bits { /** * @brief The main function implements set bit count * @param n is the number whose set bit will be counted - * @returns the count of the number set bit in the binary representation of `n` + * @returns total number of set-bits in the binary representation of number `n` */ -std::uint64_t countSetBits(int n) { - int count = 0; // "count" variable is used to count number of 1's in binary - // representation of the number - while (n != 0) { - count += n & 1; - n = n >> 1; // n=n/2 +std::uint64_t countSetBits(std :: int64_t n) { // int64_t is preferred over int so that + // no Overflow can be there. + + int count = 0; // "count" variable is used to count number of set-bits('1') in + // binary representation of number 'n' + while (n != 0) + { + ++count; + n = (n & (n - 1)); } return count; + // Why this algorithm is better than the standard one? + // Because this algorithm runs the same number of times as the number of + // set-bits in it. Means if my number is having "3" set bits, then this while loop + // will run only "3" times!! } } // namespace count_of_set_bits } // namespace bit_manipulation -/** - * @brief Self-test implementations - * @returns void - */ static void test() { // n = 4 return 1 assert(bit_manipulation::count_of_set_bits::countSetBits(4) == 1); @@ -67,9 +65,12 @@ static void test() { assert(bit_manipulation::count_of_set_bits::countSetBits(15) == 4); // n = 25 return 3 assert(bit_manipulation::count_of_set_bits::countSetBits(25) == 3); + // n = 97 return 3 + assert(bit_manipulation::count_of_set_bits::countSetBits(97) == 3); + // n = 31 return 5 + assert(bit_manipulation::count_of_set_bits::countSetBits(31) == 5); std::cout << "All test cases successfully passed!" << std::endl; } - /** * @brief Main function * @returns 0 on exit