蒟蒻求助QAQ

#include <iostream>
using namespace std;

int a[35];
int b[20];
int c[20];
int n[11];
int k;
int ans;
string s;

void dfs(int num){
    if(num>=s.length()){
        ans++;
        return ;
    }
    for(int i=1;i<=2;i++){
        int temp = a[num];
        if(i==2){
            a[num] = n[a[num]];
        }
        dfs(num+1);
        a[num] = temp;
    }
}

int main(){
    freopen("input.in","r",stdin);
    freopen("output.out","w",stdout);
    cin>>s;
    for(int i=1;i<=s.length();i++){
        a[i] = s[i] - '0';
    }
    cin>>k;
    for(int i=1;i<=k;i++){
        cin>>b[i]>>c[i];
        n[b[i]] = c[i];
    }
    dfs(1);
    cout<<ans<<endl;
    return 0;
}

不知道哪里错了，测试样例对的