# 3.3 Strings (1)

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Trie Prefix Tree Dictionary tree

Examples of LA 3942 http://acm.hust.edu.cn/vjudge/problem/22109

The first example of a dictionary tree I use set water over, first record this version, test instructions is, give a string, there are some short strings of the collection, ask how many different splitting methods so that after splitting, each substring in the collection.

Dp[len] Indicates how many split methods before Len Dp[0]=1, the first 0 characters have a split method, empty. Dp[len] is the answer, the transfer is, if the next paragraph in the collection, then you can transfer to length plus the length of the paragraph.

Starting point has la=3e5,, to each starting point, add the string may have lbi=100, all to enumerate, next is to determine whether the string exists, with hash value, O1,set query Logn, n=4000, the overall complexity la*lb*logn drifting over.

`1 //#define Txtout2 //#define DEBUG3#include <bits/stdc++.h>4 #defineMT (A, b) memset (A,b,sizeof (a))5 using namespacestd;6typedefLong LongLL;7 Const DoublePi=acos (-1.0);8 Const Doubleeps=1e-8;9 Const intinf=0x3f3f3f3f;Ten Const intm=3e5+Ten; One ConstLL mod=20071027; A classString_hash {///string Hash init o (n) query O (1) -typedef unsignedLong LongTypec;///hash value type -     Static Const intmv=3e5+Ten;///string Length the     Static Const intkey=137;///good choice of prime number of hash seed value - Typec H[MV],XP[MV]; -  Public: -     voidInitCharS[],intLS) {///incoming string array and string length +h[ls]=0; -          for(inti=ls-1; i>=0; i--) { +h[i]=h[i+1]*key+S[i]; A         } atxp[0]=1; -          for(intI=1; i<=ls; i++) { -xp[i]=xp[i-1]*key; -         } -     } -TypecGet(intPosintLen) {///incoming initial position pos, string length len, return string hash value in         returnh[pos]-h[pos+len]*Xp[len]; -     } to }hash; + intN; - CharA[m]; the Charb[4010][ the]; * LL dp[m]; \$ Set<unsignedLong Long>s;Panax Notoginseng intMax_len; - voidInit_set () { the s.clear (); +max_len=0; A      for(intI=0; i<n; i++) { the         intlb=strlen (B[i]); + Hash.init (b[i],lb); -S.insert (Hash.Get(0, LB)); \$max_len=Max (max_len,lb); \$     } - } - LL Solve () { the Init_set (); -     intlen=strlen (a);Wuyi      for(intI=0; i<=len; i++) { thedp[i]=0; -     } Wudp[0]=1; - Hash.init (A,strlen (a)); About      for(intI=0; i<len; i++) { \$         if(dp[i]==0)Continue; -          for(intj=0; j<max_len; J + +) { -             if(!s.count (Hash).Get(i,j+1)))Continue; -dp[i+j+1]+=Dp[i]; Adp[i+j+1]%=MOD; +         } the     } -     returnDp[len]; \$ } the intMain () { the #ifdef txtout theFreopen ("In.txt","R", stdin); theFreopen ("OUT.txt","W", stdout); - #endif //Txtout in     intcas=1; the      while(~SCANF ("%s%d",a,&N)) { the          for(intI=0; i<n; i++) { Aboutscanf"%s", B[i]); the         } theprintf"Case %d:%lld\n", cas++, Solve ()); the     } +     return 0; -}`
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