NOVICE43  Problem 3
When I first learned backtracking I made a program to find all the permutations of the English alphabets in lexicographically increasing. Filled with elation I showed the program to Rohil. Rohil being someone who likes to do stuff off the league was not impressed and gave me the following variation of the problem help me to solve the problem:
You have to find the number of permutations of length N (1<=N<=11) such that at whenever an alphabet (say 'c' ) appears in the permutation all the alphabets smaller than 'c' should have appeared before it at least once. An alphabet is smaller than another if it appears before the other in the English alphabet. ‘a’ being the smallest and ‘z’ being the largest. For example when N=2 then aa, ab are the only valid permutations and ba, bb is invalid since in ba all the alphabets smaller than b have not appeared at least once before it. See example for further clarification.
Input
Line 1: T (number of test cases)
Line 2: n1
Line 3: n2
…
…
Output
Line 1: number of such permutations of length n1
…
...
Example
Input: 2 2 3 Output: 2 5
Explanation for N=3, the possible permutations are: abc, aba, abb, aab, aaa
hide comments
priyanshux123:
20191228 10:09:21
Hint: Bell numbers 

sagar_june97p:
20190614 16:53:42
AC in one go.!!


megumitadokoro:
20180402 16:06:43
Basically, there are 11 possible values of n, which means you can do the backtrack. Or you can precalculate the answer and get AC in O(1). 

anubhawiiitu:
20171215 12:40:06
Answer for n=11 will be 6785** Last edit: 20171215 12:40:28 

ssunitk:
20170512 11:55:30
@Mahesh_Chandra_Sharma why its showing tle...with n^2, or O(11*11), infact it is showing tle also when i am storing the value of ans for all n=11 and then just using that array to output could u check my submissions


akshayvenkat:
20160705 20:05:20
what are the permuations for N=4 ? can someone list them out please? 

Anant Upadhyay:
20150913 17:20:33
easy! 

:.Mohib.::
20150607 15:06:42
Easy one.. ;) 

cenation:
20141216 08:53:07
easy .......... 

Levon:
20140324 17:49:49
@technophyle

Added by:  Mahesh Chandra Sharma 
Date:  20110301 
Time limit:  1s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 
Resource:  NSIT Noivce contest #4 