Unordered letter Pairs

Address:http://www.luogu.org/problem/show?pid=1341 Topic Description

Given n each of the different unordered pairs of letters (case-insensitive, the two letters in a pair of letters can be reversed). Construct a string with a n+1 letter so that each letter pair appears in the string.

Input/output format

Input format:

The first line enters a positive integer n.
The following n lines are two letters per line, indicating that the two letters need to be contiguous.

Output format:

The output string that satisfies the requirement.
If there are no strings to meet the requirements, output "no solution".
If there are multiple scenarios, please output the preceding letters with the ASCII encoding as small as possible (the dictionary order is minimal) scheme

Input/Output sample

Input Sample # #:

4aZtZXtaX

Sample # # of output:

Description

"Data size and conventions"
The number of different disordered letters is limited, and the size of n can be calculated.

Ideas

It is easy to see that this is a Eulerian graph. However, I thought for a long while will not write a graph algorithm, had to use deep search and write back, but the data is in the water, unexpectedly!

P1: I used the judgment of the heavy side.

P2: The dictionary order is required to output, then the search time from the smallest dictionary order to start the search.

varA:Array['A'..'Z','A'..'Z'] ofLongint; Du:Array['A'..'Z'] ofLongint; Ans:Array[0..100000] ofChar; N:longint;procedureDFS (u:char;tot:longint);varJ:longint;k:char;beginAns[tot]:=u; iftot=n+1  Then        begin             forj:=1  ton+1  Dowrite (ans[j]);            Writeln;        Halt End;  fork:='A'  to 'Z'  Do        ifA[u,k]<>0  Then            beginDec (a[u,k]);                Dec (A[k,u]); DFS (K,tot+1);                Inc (A[k,u]);                Inc (A[u,k]); //BacktrackingEnd;End;procedureChange ;beginFillchar (A,sizeof (a),0); Fillchar (du,sizeof (du),0);End;procedureInit;varI:longint;one,two:char;beginREADLN (n);  fori:=1  toN Do        beginreadln (One,two);            Inc (A[one,two]);            Inc (A[two,one]);            Inc (Du[one]);        Inc (Du[two]); End;End;proceduremain;varX:char;one,two:char;begin     forx:='A'  to 'Z'  Do        if(Du[x]MoD 2=1) Then            begin                ifTwo<>' '  Then                    beginWriteln ('No Solution');                    Halt End; if(one<>' ') and(two=' ') Thentwo:=x; ifOne=' '  Thenone:=x; End; if(one<>' ') and(two=' ') Then        beginWriteln ('No Solution');        Halt End; //One and two are two alternate strings, given the possibility of a heavy edgeif(one=' ') and(two=' ') Then        begin             forx:='A'  to 'Z'  Do                ifDu[x]<>0  ThenBreak ; DFS (x,1); End    Else        ifOne>two ThenDfs (both,1)        ElseDfs (one,1); //Everything for the dictionary OrderEnd;beginChange ;    Init Main;End.

View Code

Unordered letter Pairs