代码：

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int MAXn = 1e6;
const int MAXnd = MAXn * 2;
const int MAXegl = MAXnd;

int head[MAXnd + 10], cntnex, nex[MAXegl + 10], to[MAXegl + 10];
inline void Insert(int u, int v) {
	nex[++cntnex] = head[u];
	head[u] = cntnex;
	to[cntnex] = v;
}

int cntnd, last, link[MAXnd + 10], son[MAXnd + 10][26], cntep[MAXnd + 10], mxlen[MAXnd + 10];
void Init() {
	cntnd = last = 1;
}
void Extend(int ch) {
	int a, b, c;
	a = c = last, b = last = ++cntnd;
	cntep[b] = 1;
	mxlen[b] = mxlen[a] + 1;
	for (; c && !son[c][ch]; c = link[c]) son[c][ch] = b;
	if (!c) {
		link[b] = 1;
	} else {
		int d = son[c][ch];
		if (mxlen[d] == mxlen[c] + 1) {
			link[b] = d;
		} else {
			int e = ++cntnd;
			link[e] = link[d];
			// memcpy(son[e], son[d], sizeof(son[e]));
			copy(begin(son[d]), end(son[d]), begin(son[e]));
			cntep[e] = cntep[d];
			mxlen[e] = mxlen[c] + 1;
			link[d] = link[b] = e;
			for (; c && son[c][ch] == d; c = link[c]) son[c][ch] = e;
		}
	}
}

int ans;
void Dfs(int cur) {
	for (int i = head[cur]; i; i = nex[i]) {
		Dfs(to[i]);
		cntep[cur] += cntep[to[i]];
	}
	if (cntep[cur] > 1) ans = max(ans, cntep[cur] * mxlen[cur]);
}

char str[MAXn + 10]; int n;
signed main() {
	Init();
	scanf("%s", str + 1);
	n = strlen(str + 1);
	for (int i = 1; i <= n; ++i) {
		Extend(str[i] - 'a');
	}
	for (int i = 2; i <= cntnd; ++i) {
		Insert(link[i], i);
	}
	Dfs(1);
	printf("%lld\n", ans);
	return 0;
}

过不去的数据：

aabab

正确输出：

4

我的输出：

6