#include <bits/stdc++.h>
using namespace std;
void err(istream_iterator<string> it) {}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " = " << a << '\n';
  err(++it, args...);
}
long long powMod(long long x, long long y) {
  long long p = 1;
  while (y) {
    if (y % 2) {
      p = (p * x) % ((long long)1e9 + 7);
    }
    y /= 2;
    x = (x * x) % ((long long)1e9 + 7);
  }
  return p;
}
long long CpowMod(long long x, long long y, long long w) {
  long long p = 1;
  while (y) {
    if (y % 2) {
      p = (p * x) % w;
    }
    y /= 2;
    x = (x * x) % w;
  }
  return p;
}
long long invMod(long long x) { return powMod(x, ((long long)1e9 + 7) - 2); }
long long CinvMod(long long x, long long w) { return CpowMod(x, w - 2, w); }
long long gcd(long long a, long long b) { return b == 0 ? a : gcd(b, a % b); }
void solve() {
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    vector<long long> a(n, 0);
    string s;
    cin >> s;
    map<long long, set<long long> > m;
    map<long long, vector<long long> > v;
    long long num = 1;
    for (int i = 0; i <= n - 1; i++) {
      long long x = s[i] - '0';
      long long y = 1 - x;
      if ((long long)m[y].size()) {
        long long in = *m[y].rbegin();
        m[y].erase(in);
        m[x].insert(in);
        v[in].push_back(i);
      } else {
        m[x].insert(num);
        v[num].push_back(i);
        num++;
      }
    }
    for (auto &it : v) {
      for (auto &is : it.second) {
        a[is] = it.first;
      }
    }
    cout << num - 1 << '\n';
    for (auto &it : a) {
      cout << it << " ";
    }
    cout << '\n';
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cout.precision(20);
  solve();
  return 0;
}
