UVa 10054 (打印欧拉回路) The Necklace

将每个颜色看成一个顶点，对于每个珠子在两个颜色之间连一条无向边，然后求欧拉回路。

#include <cstdio>
#include <cstring>

const int maxn = 50 + 5;
int G[maxn][maxn], deg[maxn];

void Euler(int u)
{
    for(int v = 1; v <= 50; v++) if(G[u][v])
    {
        G[u][v]--; G[v][u]--;
        Euler(v);
        printf("%d %d
", v, u);
    }
}

int main()
{
    //freopen("in.txt", "r", stdin);

    int T; scanf("%d", &T);
    for(int kase = 1; kase <= T; kase++)
    {
        memset(G, 0, sizeof(G));
        memset(deg, 0, sizeof(deg));

        if(kase > 1) puts("");
        printf("Case #%d
", kase);

        int n, a, b, st;
        scanf("%d", &n);
        for(int i = 0; i < n; i++)
        {
            scanf("%d%d", &a, &b);
            st = a;
            deg[a]++; deg[b]++;
            G[a][b]++; G[b][a]++;
        }

        bool ok = true;
        for(int i = 1; i <= 50; i++) if(deg[i] % 2) { ok = false; break; }
        if(!ok) { puts("some beads may be lost"); continue; }

        Euler(st);

    }

    return 0;
}