Recently,I encountered a Runtime Error problem with C++. I wrote a code like this:

#include <bits/stdc++.h>
#define MOD 1000000007ll
#define maxn 1000000
using namespace std;

int t,num[maxn+10];
char c[maxn+10];
vector<int> v[maxn+10],res;

struct KMP {
    int n;
    vector<int> f;

    KMP(const char *s) : n(strlen(s)), f(n) {
        int p = -1;
        f[0] = -1;
        for (int i = 1; i < n; i++) {
            while (p != -1 && s[p + 1] != s[i]) p = f[p];
            if (s[p + 1] == s[i]) p++;
            f[i] = p;
        }
    }

    int &operator[](int x) {
        return f[x];
    }
} ;

inline void dfs(int x,int pr,int w)
{
	res.push_back(x);
	while(w+1<res.size()&&res[w+1]<=x/2) w++;
	num[x]=w;
	for(int i=0;i<v[x].size();i++) if(v[x][i]!=pr){
		dfs(v[x][i],x,w);
	}
	res.pop_back();
}

int main()
{
	cin>>t;
	for(int h=1;h<=t;h++)
	{
		memset(num,0,sizeof(num));
		scanf("%s",c);
		KMP f(c);
		int len=strlen(c);
		for(int i=len;i>=1;i--) f[i]=f[i-1];
		for(int i=1;i<=len;i++) f[i]++;
		for(int i=1;i<=len;i++) v[i].clear(); 
		for(int i=1;i<=len;i++){
			v[i].push_back(f[i]);
			v[f[i]].push_back(i);
		}
		int root=0;
		dfs(root,-1,-1);
		long long ans=1ll;
		for(int i=1;i<=len;i++){
			ans=ans*(long long)(num[i]+1ll);
			ans%=MOD;
		}
		if(h<t) cout<<ans<<endl;
		else cout<<ans;
	}
	return 0;
} 

When I ran this program with

1
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaxpuvf

The program showed Runtime Error.

And when I debug it, it showed: SIGTRAP trace/breakpoint trap.

So what is the problem?

Can anyone work it out?

Thanks in advance.