luogu P3946 ことりのおやつ 题解

Posted 2021-01-07 misakaazusa

题目链接：https://www.luogu.org/problemnew/show/P3946
交好几遍是因为虽然能过一直有提醒..强迫症qwq

#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int maxn = 5 * 1e6 + 10;
ll n, m, s, t, g, q;
ll dis[maxn], h[maxn], l[maxn];
bool vis[maxn];
struct edge{
    ll from, to, next, len;
}e[maxn<<2];
ll head[maxn], cnt;
queue<int> Q;
void add(ll u, ll v, ll w)
{
    e[++cnt].from = u;
    e[cnt].len = w;
    e[cnt].next = head[u];
    e[cnt].to = v;
    head[u] = cnt;
}
void SPFA()
{
    while(!Q.empty())
    {
        ll now = Q.front(); Q.pop();
        vis[now] = 0;
        for(int i = head[now]; i != -1; i = e[i].next)
        {
            //cout<<e[i].from<<" "<<e[i].to<<endl;
            if(e[i].to == t && dis[e[i].to] > dis[now] + e[i].len)
            {
                dis[e[i].to] = dis[now] + e[i].len;
                if(!vis[e[i].to])
                {
                    Q.push(e[i].to);
                    vis[e[i].to] = 1;
                }
                continue;
            }
            if(dis[e[i].to] > dis[now] + e[i].len && (dis[e[i].from] + e[i].len) * q + h[e[i].to] <= l[e[i].to])
            {
                dis[e[i].to] = dis[now] + e[i].len;
                if(!vis[e[i].to])
                {
                    Q.push(e[i].to);
                    vis[e[i].to] = 1;
                }
            }
        }
    }
}
int main()
{
    memset(dis, 127, sizeof(dis));
    memset(head, -1, sizeof(head));
    scanf("%lld%lld%lld%lld%lld%lld",&n,&m,&s,&t,&g,&q);
    for(int i = 1; i <= n; i++)
    scanf("%lld%lld",&h[i],&l[i]);
    for(int i = 1; i <= m; i++)
    {
        ll u, v, w;
        scanf("%lld%lld%lld",&u,&v,&w);
        add(u, v, w);
        add(v, u, w);
    }
    dis[s] = 0, vis[s] = 1, Q.push(s);
    SPFA();
    if(dis[t] <= g)
    printf("%lld",dis[t]);
    else
    printf("wtnap wa kotori no oyatsu desu!
");
    return 0;
}