装满的油箱

Posted 2022-07-01 programyang

算法：广搜变形(堆优化Dijkstra).

#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>

using namespace std;

typedef pair<int, int> PII;

const int N = 1010, C = 110, M = 20010;

int n, m;
int h[N], e[M], w[M], ne[M], idx;
int price[N];//每个地区的油价 
int dist[N][C];//存储距离
bool st[N][C];//判断是否走过
struct Ver

    int d, u, c;//分别表示当前点到起点的距离，当前点，当前剩余油量
    bool operator< (const Ver &W)const
    
        return d > W.d;
    
;

void add(int a, int b, int c)

    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx ++ ;


int dijkstra(int start, int end, int cap)

    memset(dist, 0x3f, sizeof dist);
    memset(st, false, sizeof st);
    priority_queue<Ver> heap;
    heap.push(0, start, 0);
    dist[start][0] = 0;

    while (heap.size())
    
        auto t = heap.top(); heap.pop();

        if (t.u == end) return t.d;//如果当前点已经是终点，返回当前点到起点的距离

        if (st[t.u][t.c]) continue;
        st[t.u][t.c] = true;

        if (t.c < cap)//如果当前剩余油量小于车的油容量
        
            if (dist[t.u][t.c + 1] > t.d + price[t.u])//当前距离可以进行更新
            
                dist[t.u][t.c + 1] = t.d + price[t.u];
                heap.push(dist[t.u][t.c + 1], t.u, t.c + 1);//更新，存入堆
            
        

        for (int i = h[t.u]; ~i; i = ne[i])//第二种情况，枚举邻点
        
            int j = e[i];
            if (t.c >= w[i])//当前剩余容量还可以到j点
            
                if (dist[j][t.c - w[i]] > t.d)//并且距离也更短
                
                    dist[j][t.c - w[i]] = t.d;//更新
                    heap.push(dist[j][t.c - w[i]], j, t.c - w[i]);
                
            
        
    

    return -1;


int main()

    scanf("%d%d", &n, &m);
    memset(h, -1, sizeof h);
    for (int i = 0; i < n; i ++ ) scanf("%d", &price[i]);
    for (int i = 0; i < m; i ++ )
    
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        add(a, b, c), add(b, a, c);
    

    int query;
    scanf("%d", &query);
    while (query -- )
    
        int a, b, c;
        scanf("%d%d%d", &c, &a, &b);
        int t = dijkstra(a, b, c);
        if (t == -1) puts("impossible");
        else printf("%d\\n", t);
    

    return 0;