#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e9 + 7;
long long binpow(long long a, long long b) {
  long long res = 1;
  while (b > 0) {
    if (b & 1) {
      res = res * a;
    }
    a = a * a;
    b >>= 1;
  }
  return res;
}
long long binpow_mod(long long a, long long b, long long c) {
  long long res = 1;
  while (b > 0) {
    if (b & 1) {
      res = res * a % c;
    }
    a = a * a % c;
    b >>= 1;
  }
  return res;
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long T;
  cin >> T;
  while (T--) {
    long long n;
    cin >> n;
    string s;
    cin >> s;
    set<long long> s1, s2;
    set<long long> c;
    long long num = 1;
    vector<long long> v;
    long long i;
    for (i = 0; i < n; i++) {
      if (s[i] == '0') {
        if (s2.size()) {
          long long ele = *s2.begin();
          v.push_back(ele);
          c.insert(ele);
          s2.erase(ele);
          s1.insert(ele);
        } else {
          v.push_back(num);
          c.insert(num);
          s1.insert(num);
          num++;
        }
      }
      if (s[i] == '1') {
        if (s1.size()) {
          long long ele = *s1.begin();
          v.push_back(ele);
          c.insert(ele);
          s1.erase(ele);
          s2.insert(ele);
        } else {
          v.push_back(num);
          c.insert(num);
          s2.insert(num);
          num++;
        }
      }
    }
    cout << c.size() << "\n";
    for (i = 0; i < v.size(); i++) {
      cout << v[i] << " ";
    }
    cout << "\n";
  }
}
