1 //#pragma comment(linker, "/STACK:16777216") //for c++ Compiler 2 #include <stdio.h> 3 #include <iostream> 4 #include <cstring> 5 #include <cmath> 6 #include <stack> 7 #include <queue> 8 #include <vector> 9 #include <algorithm>10 #define ll long long11 #define Max(a,b) (((a) > (b)) ? (a) : (b))12 #define Min(a,b) (((a) < (b)) ? (a) : (b))13 #define Abs(x) (((x) > 0) ? (x) : (-(x)))14 15 using namespace std;16 17 const int INF = 0x3f3f3f3f;18 int a[200011], ex[1000011];19 int before[1000011], after[1000011];20 21 int main(){22     int i, j ,k, t, n, m;23     int uu, vv, cur, pos;24     while(EOF != scanf("%d",&n)){25         memset(ex, 0, sizeof(ex));26         memset(before, -1, sizeof(before));27         memset(after, -1, sizeof(after));28         for(i = 1; i <= n; ++i){    29             scanf("%d%d",&uu,&vv);30             after[uu] = vv;31             before[vv] = uu;32             if(uu == 0){33                 a[2] = vv;34             } else if(vv == 0){35                 a[n - 1] = uu;36             } else{37                 ++ex[uu];38                 ++ex[vv];39             }40         }41         if(n % 2 == 0){42             cur = a[2];43             pos = 2;44             while(pos != n){45                 pos += 2;46                 cur = a[pos] = after[cur];47             }48             cur = a[n - 1];49             pos = n - 1;50             while(pos != 1){51                 pos -= 2;52                 cur = a[pos] = before[cur];53             }54         } else{55             cur = a[2];56             pos = 2;57             while(pos != n - 1){58                 pos += 2;59                 cur = a[pos] = after[cur];60             }61             for(i = 1; i <= 1000001; ++i){  //2 nums62                 if(ex[i] == 1 && before[i] == -1){63                     break;64                 }65             }66             a[1] = i;67             cur = a[1];68             pos = 1;69             while(pos != n){70                 pos += 2;71                 cur = a[pos] = after[cur];72             }73         }74 75         for(i = 1; i <= n; ++i){76             printf("%d ",a[i]);77         }78         printf("\n");79     }80     return 0;81 }82 /*83 884 3 085 5 486 1 587 0 788 11 989 9 690 6 391 7 192 593 3 094 5 395 0 596 6 497 4 298 */