Uva 11468 Substring (AC自动机)

来源：互联网发布：如何导出淘宝数据包编辑：程序博客网时间：2024/05/12 11:13

题意:给出一些字符和各自对应的选择概率,随机选择L次后将得到一个长度为L的随机字符串S.给出K个模版串,计算S不包含任何一个串的概率.

分析：构造好AC自动机后，直接在树上进行DP,dp[i[l]表示当前在i点还要匹配l长度的概率。(PS 这题精度判断好坑啊，之前保留10位疯狂WA....)

#include <queue>#include <cstdio>#include <cstring>#include <iostream>#define MAXNODE 20*21using namespace std;int T,k,n,num;char s[105];struct ACautomata{int ch[MAXNODE][62];int f[MAXNODE];bool jud[MAXNODE],vis[MAXNODE][105];double dp[MAXNODE][105];double val[62];int tot;void init(){tot = 1;memset(ch,0,sizeof(ch));memset(jud,0,sizeof(jud));memset(vis,0,sizeof(vis));memset(val,0,sizeof(val));} int idx(char c){if(c >= 'a' && c <= 'z') return c - 'a';if(c >= 'A' && c <= 'Z') return c - 'A' + 26;return c - '0' + 52;}void insert(char *s){int u = 0,n = strlen(s);for(int i = 0;i < n;i++){int c = idx(s[i]);if(!ch[u][c]) ch[u][c] = tot++;u = ch[u][c];}jud[u] = true;}void getFail(){queue<int> q;f[0] = 0;for(int c = 0;c < 62;c++){int u = ch[0][c];if(u){f[u] = 0;q.push(u);}}while(!q.empty()){int r = q.front();q.pop();for(int c = 0;c < 62;c++){int u = ch[r][c];if(!u){ch[r][c] = ch[f[r]][c];continue;}q.push(u);f[u] = ch[f[r]][c];jud[u] = jud[u] || jud[f[u]];}}}double got(int u,int l){if(jud[u]) return 0;if(l == 0) return 1.0;if(vis[u][l]) return dp[u][l];vis[u][l] = true;dp[u][l] = 0;for(int c = 0;c < 62;c++) dp[u][l] += val[c]*got(ch[u][c],l-1);return dp[u][l]; }} tree;int main(){scanf("%d",&T);while(T--){tree.init();scanf("%d",&k);for(int i = 1;i <= k;i++){scanf("%s",s);tree.insert(s);}tree.getFail();scanf("%d",&n);for(int i = 1;i <= n;i++){scanf("%s",s);scanf("%lf",&tree.val[tree.idx(s[0])]);}scanf("%d",&n);printf("Case #%d: %lf\n",++num,tree.got(0,n));}}

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