pierrechevalier83 / collatz

Playing with the collatz conjecture in C++

The collatz conjecture

The 3x+1 problem is a conjecture in mathematics which can be summarized as follows. Take any positive integer n. If n is even, divide it by 2 to get n / 2. If n is odd, multiply it by 3 and add 1 to obtain 3n + 1. Repeat the process (which has been called "Half Or Triple Plus One", or HOTPO[1]) indefinitely. The conjecture is that no matter what number you start with, you will always eventually reach 1.

This repo is an exercise in code optimization: I want to see how fast I can test this conjecture with many numbers.

Build steps

mkdir build cd build cmake -DCMAKE_BUILD_TYPE=release .. make -j8

Usage

time ./collatz 10000000 > ten_millions.txt

Current performance

Measuring the time to evaluate go throught the first ten million:

time ./collatz 10000000
100%
./collatz 10000000  3.96s user 0.79s system 99% cpu 4.750 total