UVA Planning mobile robot on Tree树上的机器人（状态压缩+bfs）

#include<bits/stdc++.h>
using namespace std;
const int maxn = 16;
const int maxe = 32;
const int MAXSTA = 491520+10; // 2^15*15
int head[maxn],to[maxe],nxt[maxe];
int ecnt;

void addEdge(int u,int v)
{
to[ecnt] = v;
nxt[ecnt] = head[u];
head[u] = ecnt++;
}

struct Node
{
int x,s;
Node(){}
Node(int X ,int S ){
x = X; s = S;
}
}q[MAXSTA];
int fa[MAXSTA],dist[MAXSTA];
struct Act
{
int u,v;
Act(int U = 0,int V = 0):u(U),v(V){}
}act[MAXSTA];
bool vis[32768][15];

int n,m,s,t,sta;

void print_ans(int u)
{
if(~fa[u])print_ans(fa[u]);
else return;
printf("%d %d\n",act[u].u+1,act[u].v+1);
}

void bfs()
{
int _front = 0,rear = 0;
q[rear].x = s; q[rear].s = sta;
fa[rear] = -1; dist[rear++] = 0;
memset(vis,0,sizeof(vis));
vis[sta][s] = true;
while(_front<rear){
Node &u = q[_front];
if(u.x == t) {
printf("%d\n",dist[_front]);
print_ans(_front);
return ;
}
for(int who = 0; who < n; who++) if(u.s>>who&1){
int newSta = u.s^(1<<who);
for(int i = head[who]; ~i; i = nxt[i]) if((u.s>>to[i]&1)^1) {
Node &v = q[rear];
v.s = newSta|1<<to[i];
v.x = who != u.x ? u.x : to[i];
if(!vis[v.s][v.x]){
vis[v.s][v.x] = true;
fa[rear] = _front;
act[rear].u = who;act[rear].v = to[i];
dist[rear++] = dist[_front] + 1;
}
}

}
_front++;
}
printf("-1\n");
}

int main()
{
//freopen("in.txt","r",stdin);
int T; scanf("%d",&T);
for(int cas = 1; cas <= T; cas++){
scanf("%d%d%d%d",&n,&m,&s,&t);
s--; t--;
sta = 1<<s;
for(int i = 0; i < m; i++) {
int t;
scanf("%d",&t);
sta |= 1<<(t-1);
}
ecnt = 0; memset(head,-1,sizeof(head));
for(int i = 1; i < n; i++){
int u,v; scanf("%d%d",&u,&v);
u--;v--;
addEdge(u,v); addEdge(v,u);
}
printf("Case %d: ",cas);
bfs();
}
return 0;
}