【Uva11468】Substring【AC自动机】【概率DP】

来源：互联网发布：男女恋爱观演变知乎编辑：程序博客网时间：2024/06/06 12:26

http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=31655

大白上的题。

AC自动机经典题型。

论如何忘记写getfail()。

/* Footprints In The Blood Soaked Snow */#include <cstdio>#include <cstring>#include <algorithm>using namespace std;typedef double DB;const int maxnode = 405, maxn = 105, maxl = 105, M = 61, maxq = 10000;const DB eps = 1e-9;int q[maxq];DB pro[maxn], dp[maxnode][maxl];bool vis[maxnode][maxl];inline int getid(char ch) {if(ch >= 'a' && ch <= 'z') return ch - 'a';if(ch >= 'A' && ch <= 'Z') return ch - 'A' + 26;if(ch >= '0' && ch <= '9') return ch - '0' + 52;}struct _acm {int son[maxnode][maxn], acmcnt, fail[maxnode];bool flag[maxnode];void init() {memset(son, 0, sizeof(son)); acmcnt = 0;for(int i = 0; i < maxnode; i++) fail[i] = flag[i] = 0;}void insert(char *s) {int now = 0, len = strlen(s);for(int i = 0; i < len; i++) {int &pos = son[now][getid(s[i])];if(!pos) pos = ++acmcnt;now = pos;}flag[now] = 1;}void getfail() {int h = 0, t = 0;for(int i = 0; i <= M; i++) if(son[0][i]) q[t++] = son[0][i];while(h != t) {int u = q[h++];for(int i = 0; i <= M; i++)if(!son[u][i]) son[u][i] = son[fail[u]][i];else {fail[q[t++] = son[u][i]] = son[fail[u]][i];flag[son[u][i]] |= flag[fail[son[u][i]]];}}}DB dfs(int u, int L) {if(!L) return 1.0;if(vis[u][L]) return dp[u][L];vis[u][L] = 1; dp[u][L] = 0.0;for(int i = 0; i <= M; i++)if(!flag[son[u][i]]) dp[u][L] += pro[i] * dfs(son[u][i], L - 1);return dp[u][L];}} acm;char str[maxn];int main() {int T; scanf("%d", &T);for(int cas = 1; cas <= T; cas++) {acm.init();memset(vis, 0, sizeof(vis));for(int i = 0; i <= M; i++) pro[i] = 0.0;int m; scanf("%d", &m);for(int i = 1; i <= m; i++) {scanf("%s", str);acm.insert(str);}acm.getfail();scanf("%d", &m);for(int i = 1; i <= m; i++) {DB x;scanf("%s%lf", str, &x);pro[getid(str[0])] = x;}scanf("%d", &m);printf("Case #%d: %.6lf\n", cas, acm.dfs(0, m));}return 0;}

0 0