Time complexity seems rather a difficult notion for people who were not professionally trained in math or computer science. I understand it informally and can high-level compare which one is better and which one is worse (say: polynomial time algorithm is more efficient/faster than exponential time algorithm), but my question is how can one roughly assess the time complexity of his/her own algorithm? A good example is the grand-canonical problem of integer factorization. Say one tries to write a new method to factor these awfully big integers. We know that the input has x-decimal digits and b-bytes. What does technically make an algorithm inefficient from the start? (say nested loops kills the program already and it's not even worth in-depth measurement? Does one need to obey certain programming rigours in order to ensure time complexity is capped at certain (reasonable) level)? Sorry if this sounds really informal and amateurish, but I am just very curious about this kind of things, though have little professional knowledge to understand it on my own.
Estimating the complexity of an algorithm by looking at code
algorithm analysis;runtime analysis