萌新刚学OI，求助

#include<cstdio>
#include<iostream>
#include<cstring>
#include<queue>
#include<algorithm>
#define N 4000017
#define ll long long
using namespace std;

char s[N];
int ch[N][26],fa[N],len[N],lst,num;
bool vis[N];
ll siz[N];

void build_trie()
{
	int n = strlen(s + 1);
	int u = 1;
	for(int i = 1;i <= n;i += 1)
	{
		int x = s[i] - 'a';
		if(!ch[u][x])ch[u][x] = ++num;
		u = ch[u][x];
	}
}

void Extend(int p,int c)
{
	len[p] = len[lst] + 1;
	int f = fa[lst];
	while(f && !ch[f][c]){
		ch[f][c] = p;
		f = fa[f];
	}
	if(!f){
		fa[p] = 1;
		return;
	}
	int x = ch[f][c];
	if(len[f] + 1 == len[x])
	{
		fa[p] = x;
		return;
	}
	int y = ++num;
	len[y] = len[f] + 1;
	fa[y] = fa[x];
	fa[p] = fa[x] = y;
	memcpy(ch[y],ch[x],sizeof(ch[y]));
	while(f && ch[f][c] == x)ch[f][c] = y,f = fa[f];
}

void bfs()
{
	queue<pair<int,int> >q;
	int u = 1;
	for(int i = 0;i < 26;i += 1)
		if(ch[u][i])q.push(make_pair(u,i));
	while(!q.empty())
	{
		int x = q.front().second;
		lst = q.front().first;
		u = ch[lst][x];
		q.pop();
		Extend(u,x);
		for(int i = 0;i < 26;i += 1)
			if(ch[u][i])q.push(make_pair(u,i));
	}
}

void dfs(int u)
{
	if(vis[u])return;
	vis[u] = 1;
	for(int i = 0;i < 26;i += 1)
	{
		int v = ch[u][i];
		if(!v)continue;
		dfs(v);
		siz[u] += siz[v];
	}
}

int main()
{
	lst = num = 1;
	int m;
	scanf("%d",&m);
	for(int i = 1;i <= m;i += 1)
	{
		scanf("%s",s + 1);
		build_trie();
	}
	bfs();
	for(int i = 2;i <= num;i += 1)
		siz[i] = 1;
	dfs(1);
	printf("%lld\n",siz[1]);
	return 0;
}