Codeforces 510 C Fox and Names "topological sort"

Test instructions: gives the name of n string, which indicates the dictionary order from small to large, in order to conform to such a string permutation of the dictionary

Iterate through the string first, and when you encounter a different time, add edge, record the corresponding degree

Then is the BFS process, if a point has not been accessed, and the degree of 0, it is added to the queue, and the node it points to the degree minus 1

In addition, if LEN[I]<LEN[I-1], the I string is the prefix of the i-1 string, but it is also in the back, so that there is no dictionary order, direct output "impossible"

1#include <iostream>2#include <cstdio>3#include <cstring>4#include <cmath>5#include <stack>6#include <vector>7#include <map>8#include <Set>9#include <queue>Ten#include <algorithm> One using namespacestd; A  -typedefLong LongLL; - Const intINF = (1<< -)-1; the Const intMod=1000000007; - Const intmaxn=100005; -  - intE[MAXN],FIRST[MAXN],NEXT[MAXN],ANS[MAXN],LEN[MAXN],VIS[MAXN],inch[MAXN]; + Chars[ the][ the]; - intecnt; +  A voidAddedges (intUintv) { ate[ecnt]=v; -next[ecnt]=First[u]; -first[u]=ecnt; -     inch[v]++; -ecnt++; - } in  - intMain () { to      + //freopen ("In.txt", "R", stdin); - //freopen ("OUT.txt", "w", stdout); the     intN; *Cin>>N; $     Panax Notoginsengmemset (first,-1,sizeof(first)); -      for(intI=1; i<=n;i++){ theCin>>S[i]; +len[i]=strlen (S[i]); A     } the      +      -     intJ; $Ecnt=0; $      for(intI=2; i<=n;i++){ -          for(j=0; J<min (len[i],len[i-1]); J + +){ -             if(s[i-1][j]!=S[i][j]) { theAddedges (s[i-1][j]-'a', s[i][j]-'a'); -                  Break;Wuyi             } the         } -         if(len[i]<len[i-1]&&j==Len[i]) { Wuprintf"impossible\n"); -             return 0; About         } $     } -      -      -memset (Vis,0,sizeof(Vis)); A      +      for(intI=1; i<= -; i++){ the         intjj= -; -         intJ; $          for(j=0;j< -; j + +){ the             if(!vis[j]&&inch[j]==0){ thevis[j]=1; theans[i]=J; the                  for(intk=first[j];k!=-1; k=Next[k]) { -                     inch[e[k]]--; in                 } thejj=J; the                  Break; About             } the         } the         if(jj== -){//The value of JJ has not changed, which means that the topological order cannot be found theprintf"impossible\n"); +             return 0;  -         } the     }Bayi      the      for(intI=1; i<= -; i++) theprintf"%c", ans[i]+'a'); -printf"\ n"); -     return 0; the}

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Codeforces 510 C Fox and Names "topological sort"