func_code_string: #include <bits/stdc++.h>   using namespace std;   long long sqr(long long x) { return x * x; }   int mysqrt(long long x) {     int l = 0, r = 1e9 + 1;     while (r - l > 1) {       int m = (l + r) / 2;       if (m * (long long)m <= x)         l = m;       else         r = m;     }     return l;   }   mt19937 rnd(1227);   mt19937_64 rndll(12365);   long long AR = 19, BR = 13, CR = 23, XR = 228, YR = 322, MODR = 1e9 + 993;   long long myrand() {     long long ZR = (XR * AR + YR * BR + CR) % MODR;     XR = YR;     YR = ZR;     return ZR;   }   const int Mod = 1e9 + 9;   int bpow(int x, int y) {     if (y == 0) return 1;     if (y == 1) return x;     int ret = bpow(x, y >> 1);     ret = (ret * (long long)ret) % Mod;     if (y & 1) ret = (ret * (long long)x) % Mod;     return ret;   }   int bdiv(int x, int y) { return (x * (long long)bpow(y, Mod - 2)) % Mod; }   void setmin(int &x, int y) { x = min(x, y); }   void setmax(int &x, int y) { x = max(x, y); }   void setmin(long long &x, long long y) { x = min(x, y); }   void setmax(long long &x, long long y) { x = max(x, y); }   int gcd(int a, int b) { return a ? gcd(b % a, a) : b; }   const long long llinf = 2e18 + 100;   const double eps = 1e-9;   const int maxn = 2e5 + 100, maxw = 1e7 + 100, inf = 2e9 + 100, sq = 300,             mod = 1e9 + 9, LG = 17;   int n;   vector<int> e[maxn];   int a[maxn];   vector<int> ans;   bool vis[maxn];   void go(int v, int par) {     ans.push_back(v);     vis[v] = 1;     for (int i : e[v])       if (i != par && !vis[i]) go(i, v);   }   void dfs(int v, int par) {     for (int i : e[v])       if (i != par) {         dfs(i, v);         if (vis[i]) a[v] ^= 1;       }     if (a[v] == 0) go(v, par);   }   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     cin >> n;     for (int i = 0; i < n; i++) {       int v = i, u;       cin >> u;       u--;       if (u >= 0) {         e[v].push_back(u);         e[u].push_back(v);         a[v] ^= 1;         a[u] ^= 1;       }     }     dfs(0, -1);     if (ans.size() < n)       cout <<  NO ;     else {       cout <<  YES n ;       for (int i : ans) cout << i + 1 <<   n ;     }   }   