这是F题的题解，有人解答一下it.second的用法吗

#include<bits/stdc++.h>

using namespace std;

int main()

{

string s;

map <char, int> cnt;

vector <char> v;

cin >> s;

for (int i = 0; i != s.size(); i++)

{

if (isdigit(s[i]))

cnt[s[i-1]] += s[i]-'0'-1;

else cnt[s[i]]++;

if (cnt[s[i]] == 1) v.push_back(s[i]);

}

int k = cnt.begin()->second;

for (auto & it : cnt)

k = gcd(k, it.second);

for (auto ch : v)

{

cout << ch;

if (cnt[ch] > 1)

cout << cnt[ch];

}

cout << " ";

for (auto ch : v)

{

cout << ch;

if (cnt[ch]/k > 1)

cout << cnt[ch]/k;

}

return 0;

}