https://vjudge.net/problem/Gym-101630J/origin

先跑一遍spfa,这样就排除了小于k条边的情况。枚举那k条边中最小的边权,然后让所有的边都减去它,接着跑spfa,然后在加上k*v[i]

#include <iostream>
#include <cstdio>
#include <queue>
#include <algorithm>
#include <cmath>
#include <cstring>
#define inf 2147483647000000
#define N 1000010
#define p(a) putchar(a)
#define For(i,a,b) for(register long long i=a;i<=b;++i)

using namespace std;
long long n,m,k,x,y,ans;
long long v[N],d[N];
bool vis[N];
deque<long long>q;
struct node{
    long long n;
    long long v;
    node *next;
}*e[N];

inline void in(long long &x){
    long long y=1;char c=getchar();x=0;
    while(c<'0'||c>'9'){if(c=='-')y=-1;c=getchar();}
    while(c<='9'&&c>='0'){ x=(x<<1)+(x<<3)+c-'0';c=getchar();}
    x*=y;
}
inline void o(long long x){
    if(x<0){p('-');x=-x;}
    if(x>9)o(x/10);
    p(x%10+'0');
}

inline void push(register long long x,register long long y,register long long v){
    node *p;
    p=new node();
    p->n=y;
    p->v=v;
    if(e[x]==0)
        e[x]=p;
    else{
        p->next=e[x]->next;
        e[x]->next=p;
    }
}

inline long long spfa(long long t){
    For(i,0,n) vis[i]=0,d[i]=inf;
    d[1]=0;
    q.push_back(1);
    while(!q.empty()){
        x=q.front();q.pop_front();
        vis[x]=1;
        for(register node *i=e[x];i;i=i->next){
            if(d[i->n]>d[x]+max((long long)0,i->v-t)){
                d[i->n]=d[x]+max((long long)0,i->v-t);
                if(!vis[i->n]){
                    vis[i->n]=1;
                    if(!q.empty()&&d[i->n]<d[q.front()]) q.push_front(i->n);
                    else q.push_back(i->n);
                }    
            }
        }

        vis[x]=0;
    }
    return d[n];
}

signed main(){
    in(n);in(m);in(k);
    For(i,1,m){
        in(x);in(y);in(v[i]);
        push(x,y,v[i]);
        push(y,x,v[i]);
    }
    ans=spfa(0);
    For(i,1,m) ans=min(ans,spfa(v[i])+k*v[i]);
    o(ans);
    return 0;
}

 

posted @ 2020-03-25 21:24  WeiAR  阅读(...)  评论(...编辑  收藏