# Luogu P3346 [ZJOI2015] fantasy land favored by gods (generalized suffix automata)

## Sol

Board questions of generalized SAM.

First, if the leaf node is no more than 20, then the subtree whose root is each leaf node can be directly inserted into the generalized SAM.

Because all legal answers must be a chain in a tree with a leaf node as its root, all legal answers can be counted

Then there's the classic essence of different substrings, \ (ans = \sum len[i] - len[fa[i]] \)

#include<bits/stdc++.h>
#define LL long long
using namespace std;
const int MAXN = 2e6 + 10;
inline 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, C, a[MAXN], deg[MAXN];
namespace SAM {
int fa[MAXN], len[MAXN], ch[MAXN][11], tot = 1, root = 1, las = 1;
int insert(int x, int pre) {
int now = ++tot; len[now] = len[pre] + 1;
for(; pre && !ch[pre][x]; pre = fa[pre]) ch[pre][x] = now;
if(!pre) {fa[now] = root; return now;}
int q = ch[pre][x];
if(len[q] == len[pre] + 1) fa[now] = q;
else {
int nq = ++tot; fa[nq] = fa[q]; len[nq] = len[pre] + 1;
memcpy(ch[nq], ch[q], sizeof(ch[q]));
for(; pre && ch[pre][x] == q; pre = fa[pre]) ch[pre][x] = nq;
fa[q] = fa[now] = nq;
}
return now;
}
LL calc() {
LL ans = 0;
for(int i = 1; i <= tot; i++) ans += len[i] - len[fa[i]];
return ans;
}
}
vector<int> v[MAXN], node;
void dfs(int x, int _fa, int p) {
p = SAM::insert(a[x], p);
for(auto &to : v[x]) {
if(to == _fa) continue;
dfs(to, x, p);
}
}
int main() {
for(int i = 1; i <= N; i++) a[i] = read();
for(int i = 1; i <= N - 1; i++) {
int x = read(), y = read();
v[x].push_back(y); deg[x]++;
v[y].push_back(x); deg[y]++;
}
for(int i = 1; i <= N; i++)
if(deg[i] == 1) SAM::las = 1, dfs(i, 0, 1);
cout << SAM::calc();
return 0;
}

Tags: C++

Posted on Mon, 02 Dec 2019 17:55:51 -0500 by CFennell