LA 3942 Remember the Word（Trie树 + dp）

https://icpcarchive.ecs.baylor.edu/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=1943

题意：给出一个由S个不同单词组成的字典和一个长字符串。把这个字符串分解成若干个单词的连接（单词可重复使用），有多少种方法？

解题思路：用Trie存入字典，设dp[i]为从字符i开始的字符串的分解方案数，

则有dp[i] = sum{dp[i+len(x)] | 单词x为S[i...L]的前缀}。

/*
 *Author:       Zhaofa Fang
 *Created time: 2013-04-02-21.55
 *Language:     C++
 */
#include <cstdio>
#include <cstdlib>
#include <sstream>
#include <iostream>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <string>
#include <utility>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
using namespace std;

typedef long long ll;
#define DEBUG(x) cout<< #x << ':' << x << endl
#define REP(i,n) for(int i=0;i < (n);i++)
#define REPD(i,n) for(int i=(n-1);i >= 0;i--)
#define FOR(i,s,t) for(int i = (s);i <= (t);i++)
#define FORD(i,s,t) for(int i = (s);i >= (t);i--)
#define PII pair<int,int>
#define PB push_back
#define MP make_pair
#define ft first
#define sd second
#define lowbit(x) (x&(-x))
#define INF (1<<30)

const int maxnode = 400111;
const int sigma_size = 26;
const int mod = 20071027;
int dp[300111];
char str[300111];
int ch[maxnode][sigma_size];
struct Trie{

    bool val[maxnode];
    int sz;
    Trie(){sz = 1;memset(ch[0],0,sizeof(ch[0]));}
    int idx(char c){return c-'a';}

    void insert(char *S){
        int u = 0, len = strlen(S);
        REP(i,len){
            int c = idx(S[i]);
            if(!ch[u][c]){
                memset(ch[sz],0,sizeof(ch[sz]));
                val[sz] = 0;
                ch[u][c] = sz++;
            }
            u = ch[u][c];
        }
        val[u] = 1;
    }

    int find(char *S,int pos){
        int ans = 0;
        int u = 0,len = strlen(S);
        for(int i=pos;i<len&&i<pos+101;i++){
            int c = idx(S[i]);
            if(!ch[u][c])return ans;
            u = ch[u][c];
            if(val[u])ans = (ans+dp[i+1])%mod;
        }
        return ans;
    }
};
int main(){
    //freopen("in","r",stdin);
    //freopen("out","w",stdout);
    int cas = 0;
    while(~scanf("%s",str)){
        int n;
        scanf("%d",&n);
        char str1[110];
        Trie pp;
        REP(i,n){
            scanf("%s",str1);
            pp.insert(str1);
        }
        int len = strlen(str);
        dp[len] = 1;
        REPD(i,len)dp[i] = pp.find(str,i);
        printf("Case %d: %d\n",++cas,dp[0]);
    }
    return 0;
}