题解

暴力打表后质数串发现只有这些数：2、3、5、7、23、37、53、73、373

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=1e6+10;
int n,m,k;
string s;
//2 3 5 7 23 37 53 73 373
//2 23
//3 37 373
//5 53
//7 73
int main(){
    ios::sync_with_stdio(0);
    int T;
    cin>>T;
    for (int cs = 1; cs <= T; ++cs) {
        cin>>n;
        cin>>s;
        int cnt=0;
        for (int i = 0; i <n; ++i) {
            if(s[i]=='2'){
                cnt++;
                if(i+1<n &&s[i+1]=='3')cnt++;
            }else if(s[i]=='3'){
                cnt++;
                if(i+1<n && s[i+1]=='7'){
                    cnt++;
                    if(i+2<n &&s[i+2]=='3') cnt++;
                }
            }else if(s[i]=='5'){
                cnt++;
                if(i+1<n && s[i+1]=='3') cnt++;
            }else if(s[i]=='7'){
                cnt++;
                if(i+1<n && s[i+1]=='3') cnt++;
            }
        }
        cout<<cnt<<endl;
    }
    return 0;
}