#include <bits/stdc++.h>
using namespace std;
long long a[200020];
long long va[200020];
long long b[200020];
long long c[200020];
char ans[200020];
char ansstring[200020];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  long long n, k;
  cin >> n >> k;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    va[a[i]] = i;
  }
  for (int i = 1; i <= n; i++) {
    cin >> b[i];
    c[i] = va[b[i]];
  }
  char ch = 'a';
  for (int i = 1; i <= n; i++) {
    long long reach = c[i];
    if (ch > 'z') {
      ch--;
    }
    for (int j = i; j <= reach; j++) {
      reach = max(reach, c[j]);
      ans[j] = ch;
    }
    i = reach;
    ch++;
  }
  if (ch - 'a' < k) {
    cout << "NO";
    return 0;
  }
  for (int i = 1; i <= n; i++) {
    ansstring[b[i]] = ans[i];
  }
  cout << "YES\n";
  for (int i = 1; i <= n; i++) {
    cout << ansstring[i];
  }
}
