k短路

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
#define MAXN 1111
#define inf 1<<30
struct Edge{
	int v,w;
	Edge(int vv,int ww):v(vv),w(ww){}
};
struct Node{
	int v,g,f;
	bool operator < (const Node &p) const {
		return p.f<f;
	}
};

vector<vector<Edge> >remap;//反图，用于求h[]的值
vector<vector<Edge> >map;

int n,m,st,ed,k,min_kth;
int g[MAXN],h[MAXN];
bool mark[MAXN];
int _count[MAXN];

void SPFA(int u)
{
	memset(mark,false,(n+2)*sizeof(int));
	for(int i=1;i<=n;i++)h[i]=inf;
	h[u]=0;
	queue<int>Q;
	Q.push(u);
	while(!Q.empty()){
		u=Q.front();
		Q.pop();
		mark[u]=false;
		for(int i=0;i<remap[u].size();i++){
			int v=remap[u][i].v,w=remap[u][i].w;
			if(h[u]+w<h[v]){
				h[v]=h[u]+w;
				if(!mark[v]){ mark[v]=true;Q.push(v); }
			}
		}
	}
}


int Astar_Kth(int st,int ed)
{
	memset(_count,0,(n+2)*sizeof(int));
	min_kth=-1;
	if(st==ed)k++;
	if(h[st]==inf)return min_kth;
	Node p,q;
	priority_queue<Node>Q;
	p.v=st,p.g=0,p.f=p.g+h[st];
	Q.push(p);
	while(!Q.empty()){
		p=Q.top();
		Q.pop();
		int u=p.v;
		_count[u]++;//当前节点的拓展次数
		if(_count[u]>k)continue;
		if(u==ed){
			if(_count[ed]==k)return min_kth=p.f;
		}
		for(int i=0;i<map[u].size();i++){
			int v=map[u][i].v,w=map[u][i].w;
			q.v=v;
			q.g=p.g+w;
			q.f=q.g+h[v];
			Q.push(q);
		}
	}
	return min_kth;
}

int main()
{
	int u,v,w;
	while(~scanf("%d%d",&n,&m)){
		remap.clear();remap.resize(n+2);
		map.clear();map.resize(n+2);
		while(m--){
			scanf("%d%d%d",&u,&v,&w);
			remap[v].push_back(Edge(u,w));
			map[u].push_back(Edge(v,w));
		}
		scanf("%d%d%d",&st,&ed,&k);
		SPFA(ed);//求h[]
		printf("%d\n",Astar_Kth(st,ed));
	}
	return 0;
}