6174

#include <iostream>
#include <cstdint>
#include <cstdint>

#include <algorithm>

using namespace std;

int K( int n){
    array<uint8_t, 4> digits;
    for (int i=0; i<4;i++){
        digits[i]=n%10;
        n/=10;
    }
    sort(begin(digits),end(digits));
    return 999*(digits[3]-digits[0]) + 90*(digits[2]-digits[1]);
}

vector<int> Distance;

void fix_distance(int i){
    if (Distance[i]!=-1)
        return; //I did nothing and my job is done
    int Next = K(i);
    fix_distance(Next);
    Distance[i]=Distance[Next]+1;
}


int main()
{
    Distance = vector<int> (10000,-1);
    Distance [ 6174] =0;
    Distance [ 0] =0;
    for (int i=0; i<size(Distance); i++){
        fix_distance(i);
    };
    cout<<"Number distance next_number\n";
    for (int i=0; i<size(Distance); i++){
        if (K(i)!=0)
            cout<<i<<" "<<Distance[i]<<" "<<K(i)<<'\n';
    };
    return 0;
}