Go: package main

import (
	"container/heap"
	"fmt"
)

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<queue>
#include<climits>

using namespace std;

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

struct Edge{
  int to,cost;
  Edge(int _to, int _cost):to(_to), cost(_cost){};
};

int minCost[110][12];
vector<Edge> edge[110];
static const int INF = INT_MAX;

int c,n,m,s,d;

int dijkstra(void){
  priority_queue<P, vector<P>, greater<P> >que;
  que.push(make_pair(0,make_pair(s,c)));

  for(int i=0;i<=n;i++)
    for(int j=0;j<=n;j++)
      minCost[i][j]=INF;

  while(!que.empty()){
    P p = que.top();
    que.pop();

    if(p.second.first==d)return p.first;
    
    for(int i=0;i<edge[p.second.first].size();i++){
      Edge e = edge[p.second.first][i];
      if(p.first+e.cost < minCost[e.to][p.second.second]){
	minCost[e.to][p.second.second] = p.first+e.cost;
	que.push(make_pair(p.first+e.cost,make_pair(e.to,p.second.second)));
      }
    }
    
    if(p.second.second==0)continue;
    
    for(int j=0;j<edge[p.second.first].size();j++){
      Edge e = edge[p.second.first][j];
      if(p.first+e.cost/2 < minCost[e.to][p.second.second-1]){
	minCost[e.to][p.second.second-1] = p.first+e.cost/2;
	que.push(make_pair(p.first+e.cost/2,make_pair(e.to,p.second.second-1)));
      }
    }
  }
  return minCost[d][0];
}

int main(void){
  int a,b,f;

  while(cin >> c >> n >> m >> s >> d,c|n|m|s|d){

    for(int i=0;i<=n;i++)edge[i].clear();

    for(int i=0;i<m;i++){
      cin >> a >> b >> f;
      edge[a].push_back(Edge(b,f));
      edge[b].push_back(Edge(a,f));
    }

    cout << dijkstra() << endl;
  }

  return 0;
}

C++: #include<queue>
#include<algorithm>
#include<iostream>
#include<string>
#include<cstdlib>
#include<cstring>
#include<cmath>
using namespace std;
int main(){
  unsigned i;
  unsigned a[100][100],b[100][11],c[100][11],m,n,o,u,v,x,y,z;
  priority_queue<pair<unsigned,pair<unsigned,unsigned> >,vector<pair<unsigned,pair<unsigned,unsigned> > >,greater<pair<unsigned,pair<unsigned,unsigned> > > > d;
  while(cin>>m>>n>>o>>u>>v&&m+n+o+u+v){
    u--;
    v--;
    memset(a,-1,sizeof(a));
    for(i=0;i<o;i++){
      int p,q,r;
      cin>>p>>q>>r;
      p--;
      q--;
      a[p][q]=a[q][p]=r;
    }
    memset(b,0,sizeof(b));
    memset(c,-1,sizeof(c));
    c[u][0]=0;
    while(d.empty()==0)
      d.pop();
    d.push(make_pair(0,make_pair(u,0)));
    for(;;){
      z=d.top().first;
      x=d.top().second.first;
      y=d.top().second.second;
      d.pop();
      if(x==v)
	break;
      if(b[x][y]==0){
	b[x][y]=1;
	for(i=0;i<n;i++){
	  if((int)a[x][i]!=-1){
	    d.push(make_pair(z+a[x][i],make_pair(i,y)));
	    if(y<m)
	      d.push(make_pair(z+a[x][i]/2,make_pair(i,y+1)));
	  }
	}
      }
    }
    cout<<z<<endl;
  }
  return 0;
}

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(){
	int c, n, m, s, d;

	cin >> c >> n >> m >> s >> d;
	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;
}