欧拉回路 USACO 3.3.1 Riding the Fences

典型的求欧拉回路，仔细一点就行了

注意

节点间可能有很多条边

/*
PROG:fence
LANG:C++
*/

#include <cstdio>
#include <algorithm>

using namespace std;

const int MAXN = 501;
int d[MAXN], tot, ans[10000], n, up, down = ~0U>>1;
int a[MAXN][MAXN];

void dfs(int x)
{
    for (int i = 1;i <= up;++i)
    {
        if (a[x][i])
        {
            --a[x][i], --a[i][x];
            dfs(i);
        }
    }
    ans[++tot] = x;
}

int main()
{
    freopen("fence.in", "r", stdin);
    freopen("fence.out", "w", stdout);
    scanf("%d", &n);
    int x, y;
    for (int i = 1;i <= n;++i)
    {
        scanf("%d%d", &x, &y);
        up = max(x, up), up = max(y, up);
        ++d[x], ++d[y];
        ++a[x][y], ++a[y][x];
    }
    for (int i = 1;i <= up;++i)
    {
        if (d[i]) down = min(i, down);
        if (d[i] & 1) { down = i; break; }
    }
    dfs(down);
    for (int i = tot;i > 0;--i)
    printf("%d\n", ans[i]);
}