I think what you are looking for is iter_swap which you can find also in <algorithm>. all you need to do is just pass two iterators each pointing at one of the elements you want to exchange. since you have the position of the two elements, you can do something like this: // assuming your … Read more
It is a matter of judgment. I will typically let std::swap do the job for prototyping code, but for release code write a custom swap. I can usually write a custom swap that is about twice as fast as 1 move construction + 2 move assignments + 1 resourceless destruction. However one may want to … Read more
Assuming what you need is a simple byte swap, try something like Unsigned 16 bit conversion: swapped = (num>>8) | (num<<8); Unsigned 32-bit conversion: swapped = ((num>>24)&0xff) | // move byte 3 to byte 0 ((num<<8)&0xff0000) | // move byte 1 to byte 2 ((num>>8)&0xff00) | // move byte 2 to byte 1 ((num<<24)&0xff000000); // … Read more
Say we have: Node1 -> Node2 -> Node3 -> Node4 -> Node5 To swap two nodes, you need to swap the next values of the ones before each of them, and also the next values of the nodes you want to swap. So to swap, say, Node2 and Node3, you effectively have to swap Node1->next … Read more
Let’s for the sake of simplicity assume you have two records id name ——— 1 john id name ——— 2 jim both from table t (but they can come from different tables) You could do UPDATE t, t as t2 SET t.id = t2.id, t2.id = t.id WHERE t.id = 1 AND t2.id = 2 … Read more
You can rotate a list in place in Python by using a deque: >>> from collections import deque >>> d=deque([1,2,3,4,5]) >>> d deque([1, 2, 3, 4, 5]) >>> d.rotate(2) >>> d deque([4, 5, 1, 2, 3]) >>> d.rotate(-2) >>> d deque([1, 2, 3, 4, 5]) Or with list slices: >>> li=[1,2,3,4,5] >>> li[2:]+li[:2] [3, 4, … Read more
I would have had to vote against your proof-of-concept implementation had it been proposed. I fear it would break the following code, which I’m pretty sure I’ve seen in the wild at least once or twice over the past dozen years. namespace oops { struct foo { foo() : i(0) {} int i; void swap(foo& … Read more
You can do this via the mlockall(2) system call under Linux; this will work for the whole process, but do read about the argument you need to pass. Do you really need to pull the whole thing in-core? If it’s a java app, you would presumably lock the whole JVM in-core. I don’t know of … Read more
The standard itself has very few mentions of iter_swap: It should have the effect of swap(*a, *b), although there is no stipulation that it must be implemented that way. The dereferenced values *a and *b must be “swappable”, which implies that swap(*a, *b) must be valid, and thus the dereferenced types must be identical, although … Read more
You could use map: map (lambda t: (t[1], t[0]), mylist) Or list comprehension: [(t[1], t[0]) for t in mylist] List comprehensions are preferred and supposedly much faster than map when lambda is needed, however note that list comprehension has a strict evaluation, that is it will be evaluated as soon as it gets bound to … Read more