P1266 速度限制 （ dij分层 + 图上dp

#include<bits/stdc++.h>
using namespace std;
using VI = vector<int>;
using ll = long long;
using PII = pair <int , int>;
const int mod = 998244353;
int n,m,d;
int idx = 0 ;
struct edge{
     int to,from;
     int next;
     int v,l;
}g[200010];
int head[200010];
void add(int a , int b , int v , int l){
    idx++;
    g[idx].from = a;
    g[idx].to = b;
    g[idx].v = v;
    g[idx].l = l;
    g[idx].next = head[a];
    head[a] = idx;
}
double dis[200][510];//达到某个点的时间 ， 速度为j
int vis[200][510];
PII fa[200][510];
double calc(int x, int y){
    return x * 1.0 / (y * 1.0);
}
int finalV;


void dij(int s){
    //时间，速度，点
    priority_queue<pair<double,PII>> pq;
    memset(dis , 126  ,sizeof dis);
    //printf("%lfn" , dis[2][25]);
    dis[1][70] = 0;
    fa[1][70] = {0,0};
    pq.push({0,{70,1}});
    while(pq.size()){
        auto x = pq.top().second;
        pq.pop();
        int v = x.first;
        int now = x.second;
        if(vis[now][v]) continue;
        vis[now][v] = 1;
        for(int i = head[now] ; i ; i = g[i].next){
            int to = g[i].to;
            int l = g[i].l;
            if(g[i].v == 0){
                if(dis[to][v] > dis[now][v] + calc(l,v)){
                    dis[to][v] = dis[now][v] + calc(l,v);
                    fa[to][v] = {now , v};
                    pq.push({-dis[to][v] ,{v,to}});
                }
            }else{
                if(dis[to][g[i].v] > dis[now][v] + calc(l ,g[i].v)){
                    dis[to][g[i].v] = dis[now][v] + calc(l ,g[i].v);
                    fa[to][g[i].v] = {now , v};
                    pq.push({-dis[to][g[i].v],{g[i].v , to}});
                }
            }

        }
    }
}

int output(int p , int v){
    if(p == 0) return 0;
    output(fa[p][v].first , fa[p][v].second);
    printf("%d " , p - 1);
    return 0;
}




int main(){
    cin>>n>>m>>d;
    d++;
    for(int i = 1 ; i <= m ; i++){
        int a,b,v,l;
        cin>>a>>b>>v>>l;
        a++,b++;
        add(a,b,v,l);
    }

    dij(1);
    int t = -1;
    for(int i = 0 ; i <= 510 ; i++){
        if(t == -1 || dis[d][t] > dis[d][i]){
            t = i;
        }
    }
    //cout<<d<<"" <<t<<"n";
    //printf("%lfn", dis[d][t]);
    //printf("%dn", fa[d][t].first);
    //cout<<dis[d][t];
    output(d , t);



}

其实并不是真的建立分层图，只是有分层图的思想，或者是dp思想在里面

dp[i][j] // 到达 i 点速度是 j 的花费

v == 0 dp[i][x] = min( dp[u][x] + calc(len[u][i] / x) )

v != 0  dp[i][v] = min( dp[u][x] + calc(len[u][i] / v) )