USACO 2.3.1 Longest Prefix --- Trie

 /* PROG:   prefix ID  :    LANG:   C++ */ #include <string.h> #include <cstdio> #include <cstdlib> #include <cstring> #include <iostream> #include <memory.h> #include <algorithm> using namespace std;  struct Trie_Node {     bool IsEnd;     Trie_Node *branch[26];     Trie_Node(): IsEnd( false )     {         memset( branch, 0, sizeof(branch) );     }// Init };  class Trie {         public:         Trie();         void Trie_Insert( char tt[] );         void Trie_Find( long j );          private:         Trie_Node *root; }t; // type class "Trie" object t  long slen; bool prefix[200400]; char line[204], ss[200400];  Trie::Trie() {     root = new Trie_Node(); }// Trie  void Trie::Trie_Insert( char tt[] ) {     Trie_Node *ptr = root;     int tlen = strlen( tt );     for ( int i=0; i<tlen; ++i )     {         if ( ptr->branch[ tt[i]-'A' ]==NULL )         {             Trie_Node *tmp = new Trie_Node();             ptr->branch[ tt[i]-'A' ] = tmp;         }                                  ptr = ptr->branch[ tt[i]-'A' ];     }                          ptr->IsEnd = true; }// Trie_Insert  void ReadData() {         while ( gets( line ) )     {         if ( line[0]=='.' ) break;                  char *tok = strtok( line, " " );         while ( tok )         {             t.Trie_Insert( tok );             //printf("%s\n", tok);             tok = strtok( NULL, " " );         }// Insert     }          char str[204];     while ( gets( str ) )     {         strcat( ss, str );     }          slen = strlen( ss );          return ; }// ReadData  void Trie::Trie_Find( long j ) {     Trie_Node *ptr = root;     for ( ; ; ++j )     {         ptr = ptr->branch[ ss[j]-'A' ];         if ( ss[j]=='\0' || ptr==NULL )             return ;         if ( ptr->IsEnd )             prefix[ j+1 ]=true;     }          return ; }// Trie_Find  void Solve() {     prefix[0] = true;     for ( long i=0; i<slen; ++i )     {         if ( !prefix[i] )   continue;                  t.Trie_Find( i );     }// Searching          int result;     for ( result=slen; !prefix[result]; --result );     printf("%d\n", result);      return ; }// Solve  int main() {     freopen("prefix.in", "r", stdin);     freopen("prefix.out", "w", stdout);      ReadData();     Solve();      //    system("pause");     return 0; }