#include <bits/stdc++.h>
using namespace std;
long long mod = pow(10, 9) + 7;
bool cmp(pair<long long, long long> x, pair<long long, long long> y) {
  if (x.first != y.first)
    return (x.first < y.first);
  else
    return x.second > y.second;
}
bool cmp2(long long x, long long y) { return y < x; }
void swap(long long *xp, long long *yp) {
  long long temp = *xp;
  *xp = *yp;
  *yp = temp;
}
const long long maxn = 1e5 + 10;
void print(vector<long long> v) {
  long long i, j, n = v.size();
  for (i = 0; i < n; i++) {
    cout << v[i] << " ";
  }
  cout << "\n";
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long lcm(long long a, long long b) { return (a * b) / gcd(a, b); }
long long power(long long x, long long y) {
  long long res = 1;
  if (x == 0) return 0;
  while (y > 0) {
    if (y & 1) res = (res * x);
    y = y / 2;
    x = (x * x);
  }
  return res;
}
int main() {
  long long int i, j, l, inc, dec, t, r;
  long long int c, d, q, e, ans = 0, temp, p, w, h, k, x, y, sum, pre, temp2, n,
                            m;
  t = 1;
  cin >> t;
  while (t--) {
    cin >> n;
    string a, b;
    cin >> a >> b;
    vector<long long> an;
    long long cnt = 0;
    long long f = 0;
    j = n - 1;
    for (i = n - 1; i >= 0; i--) {
      char ch = a[j], ch2 = a[f];
      if (cnt % 2 != 0) {
        if (ch == '1') {
          ch = '0';
        } else {
          ch = '1';
        }
        if (ch2 == '1') {
          ch2 = '0';
        } else {
          ch2 = '1';
        }
      }
      if (ch == b[i]) {
        if (cnt % 2 == 0) {
          j--;
        } else {
          j++;
        }
        continue;
      }
      if (ch2 == b[i]) an.push_back(1);
      k = abs(j - f) + 1;
      an.push_back(k);
      temp = j;
      if (cnt % 2 == 0) {
        j = f + 1;
      } else {
        j = f - 1;
      }
      f = temp;
      cnt++;
    }
    cout << an.size() << " ";
    for (i = 0; i < an.size(); i++) {
      cout << an[i] << " ";
    }
    cout << "\n";
  }
  return 0;
}
