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  1. #include <bits/stdc++.h>
  2. #define fi first
  3. #define endl '\n'
  4. #define se second
  5. #define int long long
  6. #define getName(x) #x
  7. #define vi std::vector<int>
  8. #define isz(v) (int) v.size()
  9. #define pii std::pair<int, int>
  10. #define all(v) v.begin(), v.end()
  11. #define loop cerr << "here" << endl;
  12. #define breakLoop if(TIME > 1) break;
  13. #define TIME 1.0 * clock() / CLOCKS_PER_SEC
  14. using namespace std;
  15. typedef long long ll;
  16. const int MAXN = 2e6 + 7;
  17.  
  18. template <typename T> void maximize(T &a, T b){if(a < b) a = b;}
  19. template <typename T> void minimize(T &a, T b){if(a > b) a = b;}
  20. vi save; set <int> s;
  21. int nxt[MAXN], pre[MAXN], n, ans[MAXN], start;
  22. bool check[MAXN];
  23.  
  24. signed main(){
  25.     ios::sync_with_stdio(false);
  26.     cin.tie(nullptr);
  27.     #define task "t"
  28.     if (fopen(task".inp", "r")){
  29.         freopen(task".inp", "r", stdin);
  30.         freopen(task".out", "w", stdout);
  31.     }
  32.     cin >> n;
  33.     for(int i = 1; i <= n; i++){
  34.         int x, y;
  35.         cin >> x >> y;
  36.         s.insert(x), s.insert(y);
  37.         nxt[x] = y;
  38.         pre[y] = x;
  39.         if(x == 0) start = y;
  40.     }
  41.     for(auto x : s) if(!pre[x]) save.push_back(x);
  42.     int curIdx = 2;
  43.     while(start){
  44.             check[start] = 1;
  45.         ans[curIdx] = start;
  46.         curIdx += 2;
  47.         start = nxt[start];
  48.     }
  49.     for(auto pos : save){
  50.         if(check[pos]) continue;
  51.         curIdx = 1;
  52.         int curVal = pos;
  53.         while(curVal){
  54.             ans[curIdx] = curVal;
  55.             curIdx += 2;
  56.             curVal = nxt[curVal];
  57.         }
  58.     }
  59.     for(int i = 1; i <= n; i++) cout << ans[i] << ' ';
  60. }
  61.  
Success #stdin #stdout 0s 5320KB
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https://ideone.com/7RdIQJ
language:
C++14 (gcc 8.3)
created:
22 hours ago
visibility:
public

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