【bfs優先隊列】POJ 3635

http://poj.org/problem?id=3635

#define N 1005
struct node{
    int u;
    int len;
};
vector<node> v[N];
int n,m;
int price[N];
void add(int a,int b,int w){
    node tmp;
    tmp.u = b;
    tmp.len = w;
    v[a].push_back(tmp);
    tmp.u = a;
    v[b].push_back(tmp);
}
struct Node{
    int id;//點編号
    int res;//剩餘油量
    int val;//最小花費
    friend bool operator < (Node a,Node b){
        return a.val>b.val;
    }
};
int dp[1001][101];//dp[i][j]表示到達i點後還剩j油量
bool vis[1001][101];//記錄狀态是否通路過
int bfs(int c,int s,int t){
    priority_queue<Node> pp;
    int i,j,k;
    dp[s][0] = 0;
    Node cur,next;
    cur.id = s;
    cur.res = 0;
    cur.val = 0;
    vis[s][0] = 1;
    pp.push(cur);
    while(!pp.empty()){
        cur = pp.top();
        pp.pop();
        int u = cur.id;
        int res = cur.res;
        int val = cur.val;
        vis[u][res] = 1;
        if(u == t){
            return val;
        }
        ///每個點有兩個選擇，要麼自己加油，要麼走到下一點
        if(res+1 <= c && !vis[u][res+1] && dp[u][res+1]>dp[u][res] + price[u]){
            next.id = u;
            next.res = res+1;
            next.val = dp[u][res] + price[u];
            dp[u][res+1] = dp[u][res]+price[u];
            pp.push(next);
        }
        for(i=0;i<v[u].size();i++){
            int vv = v[u][i].u;
            k = res-v[u][i].len;
            if(k<=c && k>=0 && !vis[vv][k] && val<dp[vv][k]){
                dp[vv][k] = val;
                next.id = vv;
                next.res = k;
                next.val = val;
                pp.push(next);
            }
        }
    }
    return -1;
}

int main(){
    while(scanf("%d%d",&n,&m) != -1){
        int i,j,k;
        for(i=0;i<n;i++){
            v[i].clear();
            scanf("%d",&price[i]);
        }
        while(m--){
            int a,b,w;
            scanf("%d%d%d",&a,&b,&w);
            add(a,b,w);
        }
        scanf("%d",&m);
        while(m--){
            int c,s,t;
            scanf("%d%d%d",&c,&s,&t);
            for(i=0;i<=n;i++){
                for(j=0;j<=c;j++){
                    dp[i][j] = MAX;
                    vis[i][j] = 0;
                }
            }
            int ans = bfs(c,s,t);
            if(ans==-1)puts("impossible");
            else printf("%d\n",ans);
        }
    }
    return 0;
}