This problem is a harder version of "Problem 44448. Project Euler: Problem 14 Longest Collatz sequence", because of time limits. https://ww2.mathworks.cn/matlabcentral/cody/problems/44448

The following iterative sequence is defined for the set of positive integers: n → n/2 (n is even) n → 3n + 1 (n is odd) Using the rule above and starting with 13, we generate the following sequence: 13 → 40 → 20 → 10 → 5 → 16 → 8 → 4 → 2 → 1 It can be seen that this sequence (starting at 13 and finishing at 1) contains 10 terms. Although it has not been proved yet (Collatz Problem), it is thought that all starting numbers finish at 1. Which starting number, no more than N, produces the longest chain, and how long? Don't cheat!