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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;

}
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