IITKESO207SPA4A - Lexicographic Permutations

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Problem description

Given a list of N names, find a permutation of characters of the alphabet such that these N names are in lexicographic order with respect to that permutation. If no such permutation exists, print "IMPOSSIBLE".

Lexicographical order is defined in the following way : when we compare two strings s and t, first we find teh leftmost position with differeing characters. If there is no such poisition, the shortest string is lexicographically lower. Otherwise, we compare characters according to their order in the alphabet.

Input format

An integer N for the number of names, followed by n lines each containing a string of names all in small characters.

Output format

Print the permutation of the characters such that these names are in lexicographic order. If multiple such permutations are possible, then output the one that is lexicographically lowest.

Constraints :

N will be in the set [1,1000] and each name will have length in the set [1,100]

Sample input

motwani
hopcroft
ullman
cormen
stein
rivest
leiserson

Sample output

abdefgijkmhnopqtucsrlvwxyz

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	neerajm: 2017-07-14 18:43:51 Somebody who has got it correct, please give the output of the following test case. 11 x ax ad pa pbd pbm pbe pbeq pbey pbezy pbezr Thanks in advance
	rasd: 2017-07-11 08:48:47 @ssuntik, yeah, you are right. I'll modify the answer Last edit: 2017-07-11 13:54:02
	ssunitk: 2017-07-09 16:53:57 abdefgijkmhnopqtucsrlvwxyz and abdefgijkmhucsrlnopqtvwxyz are two possible permutation of characters such that above given names are in lexicographic order , but by definition first one is lower than second and lowest among all. So i think answer for the first or sample test case should be first permutation.

Added by:	Programming Club, IITK
Date:	2017-07-06
Time limit:	1s
Source limit:	50000B
Memory limit:	1536MB
Cluster:	Cube (Intel G860)
Languages:	All
Resource:	ESO207, IIT Kanpur Summer Semester 2017