版权声明:写了自己看的,看不懂不能怪我emmmm。 https://blog.csdn.net/qq_40858062/article/details/82924413
题目链接:http://poj.org/problem?id=2449
思路:第k最短路,Astar板子题,dijkstra跑反向图的评估函数就好了。
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <bitset>
#include <cmath>
#include <cctype>
#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <map>
#include <set>
#include <sstream>
#include <iomanip>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const ll inff = 0x3f3f3f3f3f3f3f3f;
#define FOR(i,a,b) for(int i(a);i<=(b);++i)
#define FOL(i,a,b) for(int i(a);i>=(b);--i)
#define REW(a,b) memset(a,b,sizeof(a))
#define inf int(0x3f3f3f3f)
#define si(a) scanf("%d",&a)
#define sl(a) scanf("%I64d",&a)
#define sd(a) scanf("%lf",&a)
#define ss(a) scanf("%s",a)
#define mod ll(998244353)
#define pb push_back
#define eps 1e-6
#define lc d<<1
#define rc d<<1|1
#define Pll pair<ll,ll>
#define P pair<int,int>
#define pi acos(-1)
const int N=100008;
struct as{
int x;
ll v;};
ll d[N],s,t,k,cnt[N];
struct node{
ll id,dist;
bool operator<(const node a) const{
return dist+d[id]>a.dist+d[a.id];}
};
vector<as> g[N],g1[N];
void djk(int s)
{
priority_queue<P,vector<P>,greater<P> >q;
REW(d,inff);
d[s]=0;
q.push(P(d[s],s));
while(!q.empty())
{
P p=q.top();q.pop();
int v=p.second;
if(d[v]<p.first) continue;
for(int i=0;i<g1[v].size();i++)
{
as e=g1[v][i];
if(d[e.x]>d[v]+e.v)
{
d[e.x]=d[v]+e.v;
q.push(P(d[e.x],e.x));
}
}
}
}
int Astar()
{
if(d[s]==inff) return -1;
REW(cnt,0);
node tmp=node{s,0},tt;
priority_queue<node,vector<node> >qw;
qw.push(tmp);
while(!qw.empty())
{
tmp=qw.top();qw.pop();
cnt[tmp.id]++;
if(cnt[t]==k) return tmp.dist;
if(cnt[tmp.id]>k) continue;
for(int i=0;i<g[tmp.id].size();i++)
{
int v=g[tmp.id][i].x;
tt=node{v,tmp.dist+g[tmp.id][i].v};
qw.push(tt);
}
}
return -1;
}
int main()
{
cin.tie(0);
cout.tie(0);
ll n,m,x,y,z;
while(cin>>n>>m)
{
FOR(i,1,n) g[i].clear(),g1[i].clear();
FOR(i,1,m)
{
sl(x),sl(y),sl(z);
g[x].pb(as{y,z});
g1[y].pb(as{x,z});
}
cin>>s>>t>>k;
if(s==t) k++;
djk(t);
cout<<Astar()<<endl;
}
return 0;
}