uva 658 It's not a Bug, it's a Feature! 最短路

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <queue>
using namespace std;

const int maxn = (1 << 20) + 10;
const int N = 25;
const int INF = 0x3f3f3f3f;

struct Edge{
int u, d;
Edge(int u = 0, int d = 0) : u(u), d(d) {}
bool operator < (const Edge &rhs) const{
return d > rhs.d;
}
};

int n, m, t;
int bi
, pow_
;
int visit[maxn], dist[maxn];
char bug
, new_bug
;
vector<pair<int, int> > G[maxn];

void init(){
pow_[0] = 1;
for(int i = 1; i <= 21; i++)
pow_[i] = pow_[i-1] * 2;
}

void build_path(int cur){
if(cur == n){
int u = 0, v = 0;
for(int i = n - 1; i >= 0; i--){
u += bi[i] * pow_[n-1-i];
if(new_bug[i] == '+') v += pow_[n-1-i];
else if(new_bug[i] == '0') v += bi[i] * pow_[n-1-i];
}
G[u].push_back(make_pair(v, t));
//printf("%d to %d va %d\n", u, v, t);
return;
}
if(bug[cur] == '-'){
bi[cur] = 0;
build_path(cur + 1);
return;
}
if(bug[cur] == '+'){
bi[cur] = 1;
build_path(cur + 1);
return;
}
bi[cur] = 0; build_path(cur + 1);
bi[cur] = 1; build_path(cur + 1);
}

int dijkstra(){
memset(visit, 0, sizeof(visit));
memset(dist, INF, sizeof(dist));
int s = (1 << n) - 1, t = 0;
priority_queue<Edge> Q;
Q.push(Edge(s, 0));
dist[s] = 0;
while(!Q.empty()){
Edge cur = Q.top(); Q.pop();
int u = cur.u;
if(visit[u]) continue;
visit[u] = 1;
for(int i = 0; i < (int)G[u].size(); i++){
int v = G[u][i].first;
int d = G[u][i].second;
if(dist[v] > dist[u] + d){
dist[v] = dist[u] + d;
Q.push(Edge(v, dist[v]));
}
}
}
return dist[t];
}

int cas = 0;

void solve(){
for(int i = 0; i < (1 << n); i++) G[i].clear();
for(int i = 0; i < m; i++){
scanf("%d%s%s", &t, bug, new_bug);
build_path(0);
}
int ans = dijkstra();
printf("Product %d\n", ++cas);
if(ans == INF)
printf("Bugs cannot be fixed.\n\n");
else
printf("Fastest sequence takes %d seconds.\n\n", ans);
}

int main()
{
init();
while(scanf("%d%d", &n, &m) && n) solve();
return 0;
}