CF 291E. Tree-String Problem [dfs kmp trie图优化]

[CF291E](http://codeforces.com/contest/291/problem/E) 题意：一棵树，每条边上有一些字符，求目标串出现了多少次

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直接求目标串的fail然后一边dfs一边跑kmp
然后就被特殊数据卡到\(O(n^2)\)了...
因为这样kmp复杂度分析的基础就没有了，now指针可能每个孩子都减少n次
所以怒加trie图优化

貌似有人写了倍增+哈希的做法........

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;
typedef long long ll;
#define pii pair<int, int>
#define MP make_pair 
#define fir first
#define sec second
const int N=5e5+5, M=5e5+5;
int read(){
    char c=getchar();int x=0,f=1;
    while(c<'0'||c>'9'){if(c=='-')f=-1; c=getchar();}
    while(c>='0'&&c<='9'){x=x*10+c-'0'; c=getchar();}
    return x*f;
}

int n, x, f[M], len, t[M][27]; 
char ch[M], str[M];
struct edge{int v, ne; string s;}e[N];
int cnt, h[N];
inline void ins(int u, int v) {
	e[++cnt]=(edge){v, h[u], string(ch)}; h[u]=cnt;
}
int ans=0;
void dfs(int u, int p) {
	for(int i=h[u];i;i=e[i].ne) {
		int now = p, v = e[i].v;
		string &s = e[i].s;
		for(int i=0; i<(int)s.size(); i++) {
			now = t[now][s[i]-'a'];
			if(now == len) ans++, now = f[now];
		}
		dfs(v, now);
	}
}

int main() {
	//freopen("in","r",stdin);
	n=read();
	for(int i=2; i<=n; i++) x=read(), scanf("%s",ch), ins(x, i);
	scanf("%s",str+1); len=strlen(str+1);

	f[1]=0; int now=0;
	for(int i=2; i<=len; i++) {
		now = f[i-1];
		while(now && str[now+1] != str[i]) now = f[now];
		f[i] = str[now+1] == str[i] ? now+1 : 0;
	}
	for(int i=0; i<len; i++) 
		for(int j=0; j<26; j++) 
			t[i][j] = str[i+1]-'a' == j ? i+1 : t[f[i]][j];
	dfs(1, 0);
	cout << ans;
}