/**
* @brief Codeforces Round #279 (Div. 2) b
* @file b.cpp
* @author mianma
* @created 2014/11/27 15:29
* @edited 2014/11/27 20:40
* @type
* @note
*/
#include <cstdio>
#include <stack>
#include <cstring>
#include <vector>
#include <set>
using namespace std;
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) > (b) ? (b) : (a))
#define abs(a) ((a) > 0 ? (a) : (0 - (a)))
#define CLR(vec) memset(vec, 0, sizeof(vec))
#define MAXN 1000010
set<int> lft_store;
set<int> rht_store;
int n;
//int lft[MAXN];
int rht[MAXN];
int i;
int left, right, curr, tmp;
int main(void){
#ifdef DEBUG
freopen("./in", "r", stdin);
freopen("./out", "w", stdout);
#endif
scanf("%d", &n);
for(i = 0; i < n ; i++){
scanf("%d%d", &left, &right);
//lft[right] = left;
rht[left] = right;
if(left)
lft_store.insert(left);
if(right)
rht_store.insert(right);
}
for(set<int>::iterator iter = rht_store.begin(); iter != rht_store.end(); iter++){
#ifdef DEBUG
printf("match = %d\n", *iter);
#endif
lft_store.erase(*iter);
}
/*Get queue head*/
curr = *lft_store.begin();
right = rht[0];
#ifdef DEBUG
printf("curr = %d, rht = %d\n", curr, right);
#endif
do{
printf("%d ", curr);
tmp = rht[curr];
curr = right;
right = tmp;
#ifdef DEBUG
//printf("curr = %d, rht = %d\n", curr, right);
#endif
}while(right);
printf("%d\n", curr);
return 0;
}
Codeforces Round #279 (Div. 2) b
原文：http://my.oschina.net/u/572632/blog/349582