Luogu3804：[模板]后缀自动机

题面

luogu

Sol

\(sam\)然后树形\(DP\)

当时还不会拓扑排序的我

# include <bits/stdc++.h>
# define IL inline
# define RG register
# define Fill(a, b) memset(a, b, sizeof(a))
using namespace std;
typedef long long ll;
template <class Int>
IL void Input(RG Int &x){
	RG int z = 1; RG char c = getchar(); x = 0;
	for(; c < '0' || c > '9'; c = getchar()) z = c == '-' ? -1 : 1;
	for(; c >= '0' && c <= '9'; c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);
	x *= z;
}
const int maxn(2e6 + 5);
int n, trans[26][maxn], fa[maxn], len[maxn], tot = 1, last = 1, size[maxn];
ll ans;
vector <int> edge[maxn];
char s[maxn];
IL void Extend(RG int c){
	RG int np = ++tot, p = last; last = np;
	len[np] = len[p] + 1, size[np] = 1;
	while(p && !trans[c][p]) trans[c][p] = np, p = fa[p];
	if(!p) fa[np] = 1;
	else{
		RG int q = trans[c][p];
		if(len[p] + 1 == len[q]) fa[np] = q;
		else{
			RG int nq = ++tot;
			len[nq] = len[p] + 1, fa[nq] = fa[q];
			for(RG int i = 0; i < 26; ++i) trans[i][nq] = trans[i][q];
			fa[q] = fa[np] = nq;
			while(p && trans[c][p] == q) trans[c][p] = nq, p = fa[p];
		}
	}
}
IL void Dfs(RG int x){
	for(RG int l = edge[x].size(), e = 0; e < l; ++e)
		Dfs(edge[x][e]), size[x] += size[edge[x][e]];
	if(size[x] != 1) ans = max(ans, 1LL * size[x] * len[x]);
}
int main(RG int argc, RG char* argv[]){
	scanf(" %s", s), n = strlen(s);
	for(RG int i = 0; i < n; ++i) Extend(s[i] - 'a');
	for(RG int i = 2; i <= tot; ++i) edge[fa[i]].push_back(i);
	Dfs(1);
	printf("%lld\n", ans);
	return 0;
}