299D.cpp

/*
 *    J1K7_7
 *
 *    You can use my contents on a Creative Commons - Attribution 4.0 International - CC BY 4.0 License.  XD 
 *    - JASKAMAL KAINTH
 */
#include <iostream>
#include <sstream>
#include <fstream>
#include <string>
#include <vector>
#include <deque>
#include <queue>
#include <stack>
#include <set>
#include <cstring>
#include <cassert>
#include <list>
#include <map>
#include <unordered_map>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <utility>
#include <bitset>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <limits>
using namespace std;
typedef long long          ll;
typedef unsigned long long ull;
typedef long double        ld;
typedef pair<int,int>      pii;
typedef pair<ll,ll>        pll;
typedef vector<int>        vi;
typedef vector<long long>  vll;
#define left(x) 		   (x << 1)
#define right(x) 		   (x << 1) + 1
#define mid(l, r) 	       ((l + r) >> 1)
#define mp                 make_pair
#define pb                 push_back
#define all(a)             a.begin(),a.end()
#define debug(x)	       {cerr <<#x<<" = " <<x<<"\n"; }
#define debug2(x, y)       {cerr <<#x<<" = " <<x<<", "<<#y <<" = " <<y <<"\n";}
#define debug3(x, y, z)    {cerr <<#x<<" = " <<x<<", "<<#y <<" = " <<y <<", "<<#z<<" = "<<z<<"\n";}
#define debug4(x, y, z, w) {cerr <<#x<<" = " <<x<<", "<<#y <<" = " <<y <<", "<<#z<<" = "<<z<<", "<<#w << " = " <<w <<"\n";}
#define ss                 second
#define ff                 first
#define m0(x) 		       memset(x,0,sizeof(x))

const int mod=1e9+7;

template<class T> inline T gcd(T a,T b){ll t;while(b){a=a%b;t=a;a=b;b=t;}return a;}
template<class T> inline T lcm(T a,T b){return a/gcd(a,b)*b;}
template<typename T, typename S> T expo(T b, S e, const T &m){if(e <= 1)return e == 0?1: b;\
	return (e&1) == 0?expo((b*b)%m, e>>1, m): (b*expo((b*b)%m, e>>1, m))%m;}
template<typename T> T modinv(T a) { return expo(a, mod-2, mod); }

inline int nextint(){ int x; scanf("%d",&x); return x; }
inline ll nextll(){ ll x; scanf("%lld",&x); return x; }

const ll  mx_ll   = numeric_limits<ll> :: max();
const int mx_int  = numeric_limits<int> :: max();

const long double PI = (long double)(3.1415926535897932384626433832795);

inline vector<int> calculateZ(string inp)
{
	int len = inp.length();
	vector<int> Z(len);
	int left = 0;
	int right = 0;
	for(int k = 1; k < len; k++)
	{
		if(k > right)
		{
			left = right = k;
			while(right < len && inp[right] == inp[right-left])
			{
				right++;  
			}
			Z[k] = right - left;
			right--;
		}
		else
		{
			int k1 = k - left;
			// inside the Z-Box
			if(Z[k1] < right-k+1)
			{
				Z[k] = Z[k1];  
				//if the value is inside the Z-box then copy it
			}
			else
			{
				// otherwise do more comparisons
				left = k;
				while(right < len && inp[right] == inp[right-left])
				{
					right++;  
				}
				Z[k] = right-left;
				right--;
			}
		}
	}
	return Z;
	// Z[i] denotes the length of the longest substring starting from i which is also the prefix of the string.
}


const int maxn = 1e6+7;
int q[maxn];
int cnt[maxn];
int main()
{
    ios_base::sync_with_stdio(false); cin.tie(0);

	int n , m; cin >> n >> m;
	string s; cin >> s;
	int len = s.length();
	for(int i = 0; i < m; i++)
	{
		cin >> q[i];
		q[i]--;
	}
	vector<int> zs = calculateZ(s);
	for(int i = 0; i < m; i++)
	{
		cnt[q[i]]++;
		cnt[q[i]+len]--;
	}
	for(int i = 0; i+1 < m; i++)
	{
		int spannedlen = q[i]+len - q[i+1];
		if(spannedlen <= 0 )
			continue;
		// check if the spannedlen suffix is prefix or not. It should be.
		if(zs[len-spannedlen] != spannedlen)
		{
			cout << 0 << "\n";
			return 0;
		}
	}
	for(int i = 1; i < n; i++)
		cnt[i] += cnt[i-1];  
	ll ans = 1ll;
	for(int i = 0; i < n; i++)
	{
		if(!cnt[i])
			ans = (ans*26*1ll) %mod;
	}
	cout << ans << "\n";
    return 0;
}