#include <bits/stdc++.h>
#pragma GCC optimize(3)
#pragma GCC optimize(2)
using namespace std;
const int N = 2e5 + 10;
const int M = 2e5 + 100;
const int INF = 0x3f3f3f3f;
const int mod = 1e9 + 7;
int n, m, k, x, y, t;
vector<int> v[2];
char s[M];
int a[M];
void solve() {
  scanf("%d", &n);
  scanf("%s", s);
  int id = 0;
  v[0].clear(), v[1].clear();
  for (int i = 0; i < n; ++i) {
    int x = (s[i] - '0') ^ 1;
    if (v[x].empty()) {
      v[x ^ 1].push_back(++id);
      a[i] = id;
    } else {
      int k = v[x].back();
      v[x].pop_back();
      a[i] = k;
      v[x ^ 1].push_back(k);
    }
  }
  printf("%d\n", id);
  for (int i = 0; i < n - 1; ++i) printf("%d ", a[i]);
  printf("%d\n", a[n - 1]);
}
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int T = 1;
  scanf("%d", &T);
  while (T--) {
    solve();
  }
  return 0;
}
