CTRICK - Card Trick

The magician shuffles a small pack of cards, holds it face down and performs the following procedure:

  1. The top card is moved to the bottom of the pack. The new top card is dealt face up onto the table. It is the Ace of Spades.
  2. Two cards are moved one at a time from the top to the bottom. The next card is dealt face up onto the table. It is the Two of Spades.
  3. Three cards are moved one at a time…
  4. This goes on until the nth and last card turns out to be the n of Spades.

This impressive trick works if the magician knows how to arrange the cards beforehand (and knows how to give a false shuffle). Your program has to determine the initial order of the cards for a given number of cards, 1 ≤ n ≤ 20000.


On the first line of the input is a single positive integer, telling the number of test cases to follow. Each case consists of one line containing the integer n.


For each test case, output a line with the correct permutation of the values 1 to n, space separated. The first number showing the top card of the pack, etc…



2 1 4 3
3 1 4 5 2

hide comments
holmesherlock: 2017-05-19 13:38:59

easy on paper,,implementation was slightly tough

sas1905: 2017-05-11 12:42:24

n=1 ans=1 got 1 WA for this..But undoubtedly one of the best problems on BIT..!!

tsioftas: 2017-04-22 08:54:35

The constraints of n are wrong, it gets bigger than 20000. It costed me a wa (not a sigsev somehow xD)

avisheksanvas: 2017-02-02 12:22:19

BIT to the rescue _/\_

Rakend Chauhan: 2017-01-04 18:20:21

easy one with vector

king: 2016-12-18 13:01:47

Bit + binary search = AC ;)
a good one for bit

code_inception: 2016-12-12 20:45:06

a tough one with BIT

Last edit: 2016-12-12 20:46:52
Sajal Sarkar: 2016-12-01 10:29:41

got AC using BIT, now trying Segment Tree and getting TLE. Complexity of my solution using segment tree is O(n*logn) and with BIT it is O(n*logn*logn) with different constant factors, so segment tree should be performing better in time, am I missing something? Kindly help me on this.

Rahul Jain: 2016-11-25 09:47:45

For those who couldn't understand the problem, see this : https://www.youtube.com/watch?v=kP7FJGzorpI
It is similar trick.

Rahul Jain: 2016-11-24 20:39:40

Since SPOJ removed their Pyramid Clyster, even O(n^2) solutions are passing. They should modify the time limit on Cube Cluster for every problem that was for Pyramid.

Added by:Camilo Andrés Varela León
Time limit:3.279s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Languages:All except: ERL JS-RHINO NODEJS PERL6 VB.NET
Resource:Nordic Collegiate Contest 2006