#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5;
int read() {
  int x;
  scanf("%d", &x);
  return x;
}
void write(int x) {
  printf("%d\n", x);
  return;
}
int n, k, p[N], q[N], deg[N];
vector<int> v[N], tr[N];
int dfn[N], low[N], tim;
bool inq[N];
int col[N], id[N], tot;
int stk[N], t;
char ans[N];
void tarjan(int s) {
  dfn[s] = low[s] = ++tim;
  stk[++t] = s;
  inq[s] = true;
  for (auto t : v[s]) {
    if (!dfn[t]) {
      tarjan(t);
      low[s] = min(low[s], low[t]);
    } else if (inq[t])
      low[s] = min(low[s], dfn[t]);
  }
  if (dfn[s] == low[s]) {
    int cur;
    tot++;
    do {
      cur = stk[t--];
      inq[cur] = false;
      col[cur] = tot;
    } while (cur != s);
  }
}
void tpsort() {
  queue<int> q;
  for (int i = 1; i <= tot; ++i)
    if (deg[i] == 0) q.push(i);
  char base = 'a';
  while (!q.empty()) {
    int s = q.front();
    q.pop();
    ans[s] = base;
    if (base != 'z') ++base;
    for (auto t : tr[s]) {
      deg[t]--;
      if (deg[t] == 0) {
        q.push(t);
      }
    }
  }
}
void main_solve() {
  n = read(), k = read();
  for (int i = 1; i <= n; ++i) p[i] = read();
  for (int i = 1; i <= n; ++i) q[i] = read();
  for (int i = 1; i < n; ++i) {
    v[p[i]].push_back(p[i + 1]);
    v[q[i]].push_back(q[i + 1]);
  }
  for (int i = 1; i <= n; ++i) {
    if (!dfn[i]) tarjan(i);
  }
  if (tot < k) {
    puts("NO");
    return;
  }
  for (int i = 1; i <= n; ++i) {
    for (auto t : v[i]) {
      if (col[i] != col[t]) {
        tr[col[i]].push_back(col[t]);
        deg[col[t]]++;
      }
    }
  }
  puts("YES");
  tpsort();
  for (int i = 1; i <= n; ++i) {
    printf("%c", ans[col[i]]);
  }
  printf("\n");
  return;
}
signed main() {
  int T = 1;
  while (T--) main_solve();
  return 0;
}
