UVA208 Firetruck 消防车（并查集，dfs）

要输出所有路径，又要字典序，dfs最适合了，用并查集判断1和目的地是否连通即可

#include<bits/stdc++.h>
using namespace std;
const int maxn = 21;

int p[maxn],cnt[maxn];
void init(int n) {
    for(int i = 1;i <= n; i++) p[i] = i,cnt[i] = 1;
}
int Find(int x) { return p[x] == x ? x : p[x] = Find(p[x]); }

bool G0[maxn][maxn];
int G[maxn][maxn],deg[maxn];

int maxd;
int path[maxn];
bool vis[maxn];
int k,Count;
void dfs(int d,int cur)
{
    if(cur == k){
        printf("1");
        for(int i = 1; i < d; i++)
            printf(" %d",path[i]);
        puts("");
        Count++;
        return;
    }
    if(d == maxd) return;
    for(int i = 0; i < deg[cur]; i++){
        int v = G[cur][i];
        if(vis[v]) continue;
        vis[v] = 1;
        path[d] = v;
        dfs(d+1,v);
        vis[v] = 0;
    }
}

int main()
{
    //freopen("in.txt","r",stdin);
    int cas = 0;
    while(~scanf("%d",&k)){
        printf("CASE %d:
",++cas);
        int u,v,n = 0;
        init(20);
        memset(G0,0,sizeof(G0));
        memset(deg,0,sizeof(deg));
        while(scanf("%d%d",&u,&v),u){
            G0[u][v] = G0[v][u] = 1;
            n = max(n,v);
            n = max(n,u);
            int s1 = Find(u), s2 = Find(v);
            if(s1 != s2) {p[s1] = s2; cnt[s2] += cnt[s1];}
        }
        if(Find(k) != Find(1)) {printf("There are 0 routes from the firestation to streetcorner %d.
",k); continue;}
        for(int i = 1; i <= n; i++)
            for(int j = 1; j <= n; j++) if(G0[i][j]){
                G[i][deg[i]++] = j;
            }
        maxd = cnt[Find(1)] ;
        memset(vis,0,sizeof(vis));
        vis[1] = 1;
        Count = 0;
        dfs(1,1);
        printf("There are %d routes from the firestation to streetcorner %d.
",Count,k);
    }
    return 0;
}