Go: package main

import (
	"container/heap"
	"fmt"
	"runtime"
)

type Node struct {
	NowPosition          int
	DiscountTicketTCount int
	Amount               int
}

type PriorityQueueNode []*Node

func (pq PriorityQueueNode) Len() int {
	return len(pq)
}

func (pq PriorityQueueNode) Less(i, j int) bool {
	return pq[i].Amount < pq[j].Amount
}

func (pq PriorityQueueNode) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
}

func (pq *PriorityQueueNode) Push(node interface{}) {
	*pq = append(*pq, node.(*Node))
}

func (pq *PriorityQueueNode) Pop() interface{} {
	old := *pq
	n := len(old)
	item := old[n-1]
	*pq = old[0 : n-1]
	return item
}

type Point struct {
	NextPoint int
	Fee       int
}

type Memo struct {
	NowPoint             int
	DiscountTicketTCount int
}

func main() {
	var c, n, m, s, d int
	var a, b, f int

	for {
		fmt.Scan(&c, &n, &m, &s, &d)
		if c == 0 && n == 0 && m == 0 && s == 0 && d == 0 {
			break
		}
		s--
		d--
		pointMap := make([][]Point, n)
		for i := 0; i < n; i++ {
			pointMap[i] = make([]Point, 0, n)
		}
		for i := 0; i < m; i++ {
			fmt.Scan(&a, &b, &f)
			a--
			b--
			pointMap[a] = append(pointMap[a], Point{NextPoint: b, Fee: f})
			pointMap[b] = append(pointMap[b], Point{NextPoint: a, Fee: f})
		}
		pq := make(PriorityQueueNode, 0, m)
		start := Node{NowPosition: s, DiscountTicketTCount: c, Amount: 0}
		heap.Push(&pq, &start)
		memo := make(map[Memo]int)
		for len(pq) != 0 {
			now := heap.Pop(&pq).(*Node)
			if now.NowPosition == d {
				fmt.Println(now.Amount)
				break
			}
			memo[Memo{NowPoint: now.NowPosition, DiscountTicketTCount: now.DiscountTicketTCount}] = now.Amount
			for _, v := range pointMap[now.NowPosition] {
				next := &Node{v.NextPoint, now.DiscountTicketTCount, now.Amount + v.Fee}
				if memoAmount, ok := memo[Memo{NowPoint: v.NextPoint, DiscountTicketTCount: now.DiscountTicketTCount}]; !ok || (ok && memoAmount > next.Amount) {
					memo[Memo{NowPoint: v.NextPoint, DiscountTicketTCount: now.DiscountTicketTCount}] = next.Amount
					heap.Push(&pq, next)
				}
				if now.DiscountTicketTCount > 0 {
					next = &Node{v.NextPoint, now.DiscountTicketTCount - 1, now.Amount + v.Fee/2}
					if memoAmount, ok := memo[Memo{NowPoint: v.NextPoint, DiscountTicketTCount: now.DiscountTicketTCount}]; !ok || (ok && memoAmount > next.Amount) {
						memo[Memo{NowPoint: v.NextPoint, DiscountTicketTCount: now.DiscountTicketTCount}] = next.Amount
						heap.Push(&pq, next)
					}
				}
			}
		}
		runtime.GC()
	}
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <cstring>
#include <cstdio>
#include <queue>
#include <stack>
#include <map>
#include <set>

#define rep(i, n) for(int i = 0; i < (n); i++)
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define all(v) (v).begin(), (v).end()
#define rev(s) string((s).rbegin(), (s).rend())
#define MP make_pair
#define X first
#define Y second

using namespace std;

typedef long long ll;
typedef pair<int, int> P;

const int INF = 10000;


class V{
public:
	int total;
	int ticket;
	int to;
};
bool operator>(const V &lh, const V &rh){
	return (lh.total > rh.total);
}


int main(){
	while(1){

		int c, n, m, s, d;
		cin >> c >> n >> m >> s >> d;
		if(!(c+n+m+s+d))break;
		n++;
		vector<vector<int> > fare(n, vector<int>(n, INF));
		rep(i, m){
			int a, b, f;
			cin >> a >> b >> f;
			fare[a][b] = fare[b][a] = f;
		}

		vector<vector<int> > done(c+1, vector<int>(n, 0));	// 確定済みか
		vector<vector<int> > best(c+1, vector<int>(n, INF));	// 最短

		V start;
		start.total = 0;
		start.ticket = 0;
		start.to = s;

		priority_queue<V, vector<V>, greater<V> > q;
		q.push(start);

		while(!q.empty()){
			V p = q.top();
			q.pop();

			if(done[p.ticket][p.to] != 0) continue;
			done[p.ticket][p.to] = 1;
			best[p.ticket][p.to] = p.total;

			rep(i, n){
				if(fare[p.to][i] == INF ) continue;
				V next;
				next.total = best[p.ticket][p.to] + fare[p.to][i];
				next.ticket = p.ticket;
				next.to = i;
				q.push(next);
				if(p.ticket < c){
					next.total = best[p.ticket][p.to] + fare[p.to][i]/2;
					next.ticket = p.ticket+1;
					next.to = i;
					q.push(next);
				}
			}
		}
		//rep(i, c+1){
		//	rep(j, n){
		//		printf("%5d", best[i][j]);
		//	}
		//	cout << endl;
		//}

		cout << best[c][d] << endl;
	}

	return 0;
}

C++: #include<vector>
#include<list>
#include<algorithm>
#include<iostream>
#include<string>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
using namespace std;
int f(int a[][101],int b[],int c[],int d,int n,int p,int e,int w){
  int h,i;
  int z[101];
  int sm,mn=-1;
  if(p==e){
    do{
      h=0;
      for(i=1;i<d;i++){
	if(c[i-1]<c[i]){
	  swap(c[i-1],c[i]);
	  h=1;
	}
      }
    }while(h);
    sm=0;
    for(i=0;i<d;i++)
      sm+=i<w?c[i]/2:c[i];
    return sm;
  }
  if(b[p])
    return -1;
  memcpy(z,b,sizeof(z));
  z[p]=1;
  for(i=1;i<n+1;i++){
    if(a[p][i]!=-1){
      int tmp;
      c[d]=a[p][i];
      if((tmp=f(a,z,c,d+1,n,i,e,w))!=-1){
	if(mn==-1||mn>tmp)
	  mn=tmp;
      }
    }
  }
  return mn;
}
int main(){
  int h,i,j,k;
  int a[101][101],b[101],c[99],g[101],w,m,n,s,e;
  memset(b,0,sizeof(b));
  while(cin>>w>>n>>m>>s>>e&&w+n+m+s+e!=0){
    memset(a,-1,sizeof(a));
    memset(g,0,sizeof(g));
    for(i=0;i<m;i++){
      int p,q,r;
      cin>>p>>q>>r;
      a[p][q]=r;
      a[q][p]=r;
      g[p]++;
      g[q]++;
    }
    do{
      h=0;
      for(i=1;i<n+1;i++){
	if(i!=s&&i!=e){
	  if(g[i]==1){
	    for(j=1;a[i][j]==-1;j++);
	    a[i][j]=-1;
	    a[j][i]=-1;
	    g[i]--;
	    g[j]--;
	    h=1;
	  }else if(g[i]==2){
	    for(j=1;a[i][j]==-1;j++);
	    for(k=j+1;a[i][k]==-1;k++);
	    if(a[j][k]!=-1&&a[j][k]<=a[i][j]+a[i][k]){
	      a[i][j]=-1;
	      a[j][j]=-1;
	      a[i][k]=-1;
	      a[k][i]=-1;
	      g[i]=0;
	      g[j]--;
	      g[k]--;
	      h=1;
	    }
	  }
	}
      }
    }while(h);
    cout<<f(a,b,c,0,n,s,e,w)<<endl;
  }
  return 0;
}

C++: #include<iostream>
#include<utility>
#include<vector>
#include<cstdio>
#include<queue>
#include <map>
using namespace std;
typedef pair<int, int> P;
typedef pair<int, P> PP;
//int in(){int x;cin>>x;return x;}

int main ()
{
	int c,n,m,s,d;
	while(cin>>c>>n>>m>>s>>d&&c&&n&&m&&s&&d)
	{
		int flg[110]={};
		int ans =0;
		priority_queue < PP, vector<PP>, greater<PP> > q;
		vector< pair< int,int > > way[110];
		for(int i=0;i<m;i++)
		{
			int a,b,f;
			cin>>a>>b>>f;
			way[a].push_back(pair<int,int>(b,f));
			way[b].push_back(pair<int,int>(a,f));
		}
		pair< int , pair<int,int> > next;
		next.first=0;next.second.first=s;next.second.second=c;
		q.push(next);
		while(!q.empty())
		{
			pair< int , pair<int,int> > now=q.top();q.pop();
			flg[now.second.first]=1;
			if(now.second.first==d)
			{
				ans=now.first;
				break;
			}
			
			for(int i=0;i<way[now.second.first].size();i++)
			{
				if(flg[way[now.second.first][i].first]==1)continue;
				next.first=now.first+way[now.second.first][i].second;
				next.second.first=way[now.second.first][i].first;
				q.push(next);
				if(now.second.second==0)continue;
				next.first=now.first+way[now.second.first][i].second/2;
				next.second.first=way[now.second.first][i].first;
				next.second.second=now.second.second-1;
				q.push(next);
			}
			
		}
		cout<<ans<<endl;
	}
	
	
	return 0;
}