求助

#define N 100100
using namespace std;

int k,cnt[10],cur[10],dp[N][3][10];
bool flg[N][10];
string s;

void modify(int i,int j,int prei,int prej,int k)
{
    int tmp[10];
    for (int t=0;t<10;t++) tmp[t]=dp[prei][prej][t];
    tmp[k]++;
    bool flag=0;
    for (int t=9;~t;t--)
    {
        if (tmp[t]>dp[i][j][t])
        {
            flag=1;break;
        }
        else if (tmp[t]<dp[i][j][t])
            break;
    }
    if (flag)
    {
        for (int t=0;t<10;t++)
            dp[i][j][t]=tmp[t];
        flg[i][j]=1;
    }
}

int main()
{
    int t;
    cin>>t;
    while (t--)
    {
        cin>>s>>k;
        memset(cnt,0,sizeof(cnt));
        memset(dp,0,sizeof(dp));
        memset(flg,0,sizeof(flg));
        int n=s.length();
        for (int i=0;i<n;i++) cnt[s[i]-'0']++;
        for (int i=9;~i;i--)
        {
            if (cnt[i]>0 && !flg[1][i%3])
            {
                flg[1][i%3]=1;
                dp[1][i%3][i]=1;
            }
        }
        for (int i=1;i<k;i++)
        {
            for (int j=0;j<3;j++)
            {
                if (!flg[i][j]) continue;
                for (int k=0;k<10;k++) cur[k]=dp[i][j][k];
                for (int k=9;~k;k--)
                {
                    if (cnt[k]>cur[k])
                    {
                        modify(i+1,(j+k)%3,i,j,k);
                    }
                }
            }
        }
        bool flag=0;
        for (int i=9;~i;i--)
        {
            if (!flag && i==0 && k>1)
            {
                break;
            }
            while (dp[k][0][i]--)
            {
                flag=1;
                cout<<i;
            }
        }
        if (!flag) cout<<-1<<endl; else cout<<endl;
    }
    return 0;
}