POJ 2337 Catenyms (有向图欧拉通路)

dog.gopher

gopher.rat

rat.tiger

aloha.aloha

arachnid.dog

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
struct EDGE
{
    char s[25];
    int x, y; 
}e[1005];
bool has[30], vis[1005];
int in[30], out[30], fa[30], ans[1005];
int n, st, len;

bool cmp(EDGE a, EDGE b)
{
    return strcmp(a.s, b.s) < 0;
}

int abs(int x)
{
    return x > 0 ? x : -x;
}

int change(char ch)
{
    return int(ch - 'a' + 1);
}

void UF_set()
{
    for(int i = 0; i < 200; i++)
        fa[i] = i;
}

int Find(int x)
{
    return fa[x] == x ? x : fa[x] = Find(fa[x]);
}

void Union(int a, int b)
{
    int r1 = Find(a);
    int r2 = Find(b);
    if(r1 != r2)
        fa[r1] = r2;
}

bool exist()
{
    int t = -1;
    for(int i = 1; i <= 26; i++)
    {
        if(has[i])
        {
            if(t == -1)
                t = Find(i);
            if(t != Find(i))
                return false;
        }
    }
    int sum = 0, tmp = 100;
    for(int i = 1; i <= 26; i++)
    {
        if(has[i])
        {
            tmp = min(tmp, i);
            if(in[i] != out[i])
            {
                if(abs(in[i] - out[i]) > 1)
                    return false;
                if(out[i] > in[i])
                    st = i;
                sum ++;
            }
        }
    }
    if(sum > 2)
        return false;
    if(sum == 0)
        st = tmp;
    return true;
}

void DFS(int now)
{
    for(int i = 0; i < n; i++)
    {
        if(!vis[i] && e[i].x == now)
        {
            vis[i] = true;
            DFS(e[i].y);
            ans[len++] = i;
        }
    }
}

int main()
{
    int T;
    scanf("%d", &T);
    while(T--)
    {
        st = 0;
        UF_set();
        memset(has, false, sizeof(has));
        memset(in, 0, sizeof(in));
        memset(out, 0, sizeof(out));
        scanf("%d", &n);
        for(int i = 0; i < n; i++)
        {
            scanf("%s", e[i].s);
            e[i].x = change(e[i].s[0]);
            e[i].y = change(e[i].s[(int)strlen(e[i].s) - 1]);
            has[e[i].x] = true;
            has[e[i].y] = true;
            in[e[i].y] ++;
            out[e[i].x] ++;
            Union(e[i].x, e[i].y);
        }
        sort(e, e + n, cmp);
        if(exist())
        {
            len = 0;
            memset(vis, false, sizeof(vis));
            DFS(st);
            for(int i = len - 1; i > 0; i--)
                printf("%s.", e[ans[i]].s);
            printf("%s\n", e[ans[0]].s);
        }
        else
            printf("***\n");
    }
}