#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long int n, k;
  cin >> n >> k;
  vector<long long int> p(n), q(n);
  for (long long int i = 0; i <= n - 1; i++) cin >> p[i];
  for (long long int i = 0; i <= n - 1; i++) cin >> q[i];
  set<long long int> p1, q1;
  vector<long long int> chan(n + 1, 0);
  long long int cou = 1;
  for (long long int i = 0; i <= n - 1; i++) {
    if (p1.find(q[i]) != p1.end())
      p1.erase(p1.find(q[i]));
    else
      q1.insert(q[i]);
    if (q1.find(p[i]) != q1.end())
      q1.erase(q1.find(p[i]));
    else
      p1.insert(p[i]);
    if (p1.empty() && q1.empty()) {
      chan[i + 1] = cou;
      cou++;
    }
  }
  for (long long int i = 1; i <= n - 1; i++) {
    chan[i] = max(chan[i], chan[i - 1]);
    chan[i] = min(chan[i], k - 1);
  }
  if (chan[n - 1] == k - 1) {
    cout << "YES" << '\n';
    vector<char> ans(n);
    for (long long int i = 0; i <= n - 1; i++) {
      ans[p[i] - 1] = 'a' + chan[i];
    }
    for (long long int i = 0; i <= n - 1; i++) cout << ans[i];
  } else {
    cout << "NO" << '\n';
  }
  return 0;
}
