I'll try my hand at a "plain english" explanation of an O(n^2) algorithm. It's a function which takes a list of numbers as inputs. You give it a list of two n

I'll try my hand at a "plain english" explanation of an O(n^2) algorithm. It's a function which takes a list of numbers as inputs. You give it a list of two numbers. It executes four operations before terminating. You give it a list of three numbers. It executes nine operations before terminating. You give it a list of four numbers. It executes sixteen operations before terminating. You see how the time required grows as n^2 with respect to the input? That's an O(n^2) algorithm, and that's why such an algorithm can be bad. A list of 1,000,000 numbers would require a trillion operations. The way this can happen is if you write a double-for loop: for x in input: for y in input: ... So, there you go. You probably won't get any plainer of an explanation without becoming oversimplified and losing meaning.