swap

Follow-up question of: Python swap indexes using slices r = ['1', '2', '3', '4', '5', '6', '7', '8'] If I want to swap slices, using a function, what would be the correct method? def swap(from,to): r[a:b+1], r[c+1:d] = r[c:d], r[a:b] swap(a:b,c:d) I want to swap the numbers 3 + 4 with 5 + 6 + 7 in r: swap(2:4,4:7) Is this correct? Without any calculation, you can do : def swap(r,a,b,c,d): assert a<=b<=c<=d r[a:d]=r[c:d]+r[b:c]+r[a:b] An interesting (but silly one, the one by B. M. is clearly better) solution would be to create an object that supports slicing: class _Swapper(object): def __init

I am stuck on problem http://www.codechef.com/JULY12/problems/LEBOBBLE Here it is required to find number of expected swaps. I tried an O(n^2) solution but it is timing out. The code is like: swaps = 0 for(i = 0;i < n-1;i++) for(j = i+1;j<n;j++) { swaps += expected swap of A[i] and A[j] } Since probabilities of elements are varying, so every pair is needed to be compared. So according to me the above code snippet must be most efficient but it is timing out. Can it be done in O(nlogn) or it any complexity better than O(n^2). Give me any hint if possible. Alright, let's think about this. We

#include <stdio.h> void swap1(int a, int b) { int temp = a; a = b; b = temp; } void swap2(int *a, int *b) { int *temp = a; a = b; b = temp; } void swap3(int *a, int *b) { int temp = *a; *a = *b; *b = temp; } main() { int a = 9, b = 4; printf("%d , %d\n", a, b); swap1(a, b); printf("%d , %d\n", a, b); swap2(&a, &b); printf("%d , %d\n", a, b); swap3(&a, &b); printf("%d , %d\n", a, b); } C has value semantics for function parameters. This means the a and b for all your three swap variants are local variables of the respective functions. They are copies of the values you pass as arguments. In

I want to maintain order of the elements being added in a list. So, I used a LinkedList in Java. Now I want to be able to swap two elements in the linked list. First of all, I cannot find an elementAt() for LinkedList . Also, there is no way to add element at a specified position. There is a Collections.swap(List<?> list, int i, int j) that you can use to swap two elements of a List<?> . There's also LinkedList.get(int index) and LinkedList.add(int index, E element) (both are methods specified by interface List ). All of these operations will be O(N) since a LinkedList does not implements

void swap(int* a, int* b) { if (a != b) *a ^= *b ^= *a ^= *b; } As the above *a ^= *b ^= *a ^= *b is just a shortcut for *a = *a ^ (*b = *b ^ (*a = *a ^ *b)) , could (e.g.) the 2nd *a be evaluated (for the XOR) just before the 3rd *a is modified (by the =)? Does it matter whether I write it in C99/C11/C++98/C++11? The C++11 standard says: 5.17/1: The assignment operator (=) and the compound assignment operators all group right-to-left . (...) the assignment is sequenced after the value computation of the right and left operands, and before the value computation of the assignment expression. 1

Swap，即交换区，除了安装Linux的时候，有多少人关心过它呢？其实，Swap的调整对Linux服务器，特别是Web服务器的性能至关重要。通过调整Swap，有时可以越过系统性能瓶颈，节省系统升级费用。 Swap的原理是一个较复杂的问题，需要大量的篇幅来说明。在这里只作简单的介绍，在以后的文章中将和大家详细讨论Swap实现的细节。 众所周知，现代操作系统都实现了“虚拟内存”这一技术，不但在功能上突破了物理内存的限制，使程序可以操纵大于实际物理内存的空间，更重要的是，“虚拟内存”是隔离每个进程的安全保护网，使每个进程都不受其它程序的干扰。 Swap空间的作用可简单描述为：当系统的物理内存不够用的时候，就需要将物理内存中的一部分空间释放出来，以供当前运行的程序使用。那些被释放的空间可能来自一些很长时间没有什么操作的程序，这些被释放的空间被临时保存到Swap空间中，等到那些程序要运行时，再从Swap中恢复保存的数据到内存中。这样，系统总是在物理内存不够时，才进行Swap交换。 计算机用户会经常遇这种现象。例如，在使用Windows系统时，可以同时运行多个程序，当你切换到一个很长时间没有理会的程序时，会听到硬盘“哗哗”直响。这是因为这个程序的内存被那些频繁运行的程序给“偷走”了，放到了Swap区中。因此，一旦此程序被放置到前端，它就会从Swap区取回自己的数据，将其放进内存，然后接着运行。

I have array like: array( 0 => 'a', 1 => 'b', 2 => 'c' ); I need to convert it to: array( 'a', 'b', 'c' ); What's the fastest way to swap keys with values? Haim Evgi PHP has the array_flip function which exchanges all keys with their corresponding values, but you do not need it in your case because the arrays are the same. array( 'a', 'b', 'c' ); This array has the keys 0, 1, and 2. Use array_flip() . That will do to swap keys with values. However, your array is OK the way it is. That is, you don't need to swap them, because then your array will become: array( 'a' => 0, 'b' => 1, 'c' => 2 );