[CF #290-c] Fox and Names (topological sort)

Title Link: Http://codeforces.com/contest/510/problem/C

The main idea: to construct an alphabet so that your alphabet can satisfy the input is sorted by dictionary order.

Recursive build: Vertically cut down and connect the first x letters of each name from top to bottom to create a diagram. Then the topology is sorted.

The reason to sort the topology, because to judge in the x-1 there is a-->b in X has b-->a, so that a ring formed. In this way, the alphabet cannot be constructed.

"Lessons Learned": Two arrays are opened in a recursive map function to record the first occurrence and last occurrence of the letter. The result is re on 12. Try not to open an array in a recursive function in the future.

1#include <cstdio>2#include <algorithm>3#include <bitset>4#include <Set>5#include <vector>6#include <iterator>7#include <cstring>8#include <map>9#include <cctype>Ten#include <iostream> One#include <string> A#include <stdexcept> - using namespacestd; -  the intN; - stringnames[111]; - BOOLHasans =true; -vector<int> g[ -]; + intc[ -],topo[ -],t; -  + voidSolveintLintRintx) { A     if(L&GT;=R)return; at     if(!hasans)return; -      for(inti=l;i<=r;i++){ -         if(x>=names[i].size ()) { -Hasans =false; -             return; -         } in         intj = i+1; -          for(; j<=r;j++){ to             if(names[i][x]==Names[j][x]) { +                 Continue; -}Else { the                  Break; *             } $         }Panax Notoginseng          while(Names[i].size ()-1<x+1&&i<j-1) i++; -Solve (i,j-1, x+1); thei = j1; +     } A  the      for(inti=l;i<r;i++) { +         if(names[i][x]==names[i+1][X])Continue; -g[names[i][x]-'a'].push_back (names[i+1][x]-'a'); $     } $ } -  - BOOLDfsintu) { theC[u] =-1; -      for(intI=0; I<g[u].size (); i++){Wuyi         intv =G[u][i]; the         if(v<0)Continue; -         if(c[v]<0)return false; Wu         Else if(!c[v] &&!dfs (v))return false; -     } AboutC[u] =1; TOPO[--T] =u; $     return true; - } -  - BOOLToposort () { At = -; +Memset (c,0,sizeof(c)); the      for(intu= -; u>=0; u--)if(!C[u]) -         if(!dfs (U))return false; $     return true; the } the  the intMain () { theCIN >>N; -      for(intI=0; i<n;i++) Cin >>Names[i]; inSolve0, N-1,0); the     if( !Hasans) { thePuts"Impossible"); About         return 0; the     } the     BOOLHasans =Toposort (); the     if( !Hasans) { +Puts"Impossible"); -         return 0; the     }Bayi      for(intI=0;i< -; i++){ thePutchar ('a'+topo[i]); the     } -Puts""); -  the     return 0; the}

[CF #290-c] Fox and Names (topological sort)