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<algorithm>
#include<queue>
#include<vector>
#define REP(i,s,n) for(int i=s;i<n;i++)
#define rep(i,n) REP(i,0,n)
#define F first
#define S second
using namespace std;
typedef pair<int,int> P;// F -> to, S -> cost
typedef pair<P,int> PP;// F->P(to,cost), S->discount
int c,n,m,s,d;
vector<PP> vec[1000];
int MD[600][13];
const int INF = 100000;

void dijkstra(){
  priority_queue<PP,vector<PP>,greater<PP> > que;
  rep(i,600)rep(j,13)MD[i][j] = INF;
  //syokika
  MD[s][c] = 0;
  que.push(PP(P(0,s),c));//dis,start,discount

  while(!que.empty() ){
    PP p = que.top();que.pop(); //priority_queのPPと
    int v = p.F.S;
    
    for(int i=0;i<vec[v].size();i++){
      PP po = vec[v][i]; //vectorのPPは意味が違うので注意！！！
      //if(MD[v][po.S] < po.F.S)continue;
      if(MD[po.F.F][c] > MD[v][c] + po.F.S){
	MD[po.F.F][c] = MD[v][c]+po.F.S;
	que.push(PP(P(MD[po.F.F][c],po.F.F),c));
      }
      if(po.S > 0 && MD[po.F.F][p.S-1] > MD[v][p.S] + po.F.S/2 ){
	MD[po.F.F][p.S-1] = MD[v][p.S]+po.F.S/2;
	que.push(PP(P(MD[po.F.F][p.S-1],po.F.F),p.S-1));
      }

    }


  }



}


int main(){
  int x,y,co;
  while(true){
    cin >> c >> n >> m >> s >> d;
    if(c+n+m+s+d == 0)break;
    rep(i,1000)vec[i].clear();
    rep(i,m){
      cin >> x >> y >> co;
      vec[x].push_back(PP(P(y,co),c));
      vec[y].push_back(PP(P(x,co),c));
    }
    dijkstra();
    int ans = INF;
    for(int i=0;i<=c;i++){
      ans = min(ans,MD[d][i]);
    }
    cout << ans << endl;
  }
  return 0;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
#include<utility>
#include<string>
#include<cmath>
#include<cstring>
#include<queue>
#include<map>
#include<climits>
#include<queue>

#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define FORR(i, m, n) for(int i = m;i >= n;i--)
#define SORT(v, n) sort(v, v+n);
#define VSORT(v) sort(v.begin(), v.end());
#define llong long long
#define pb(a) push_back(a)
using namespace std;
typedef pair<int, int> P;
typedef long long int ll;
typedef pair<ll,ll> LLP;
int dx[4] = {1,0,0,-1};
int dy[4] = {0,1,-1,0};
#define INF 1000000007
#define MOD 1000000007
#define ARRAY_MAX 105
#define TICKET 15

int c,n,m,s,d;
vector<P> G[ARRAY_MAX];//to,cost
int cost[TICKET][ARRAY_MAX];//チケットの残り枚数、最短距離
bool used[TICKET][ARRAY_MAX];


void solve(){

    cost[c][s] = 0;//出発点
    priority_queue<pair<int,P>,vector<pair<int,P> >,greater<pair<int,P> > > que;
    que.push(pair<int,P>(0,P(s,c)));//コスト、現在位置、残りのチケット枚数
    while(!que.empty()){

        pair<int,P> tmp = que.top();
        que.pop();
        int now_position = tmp.second.first;//現在位置
        int now_ticket = tmp.second.second;//残りのチケット枚数
        int now_cost = tmp.first;//次の町までのコスト

        if(cost[now_ticket][now_position] < now_cost){
            continue;
        }


        for(int i = 0;i < G[now_position].size();i++){
            //チケットを使わない場合
            if(cost[now_ticket][G[now_position][i].first] > cost[now_ticket][now_position] + G[now_position][i].second){
                cost[now_ticket][G[now_position][i].first] = cost[now_ticket][now_position] + G[now_position][i].second;
                que.push(pair<int,P>(cost[now_ticket][G[now_position][i].first],P(G[now_position][i].first,now_ticket)));
            }
            //チケットをc枚まで使う場合
            if(now_ticket > 0){
                if(cost[now_ticket-1][G[now_position][i].first] > cost[now_ticket][now_position] + G[now_position][i].second/2){
                    cost[now_ticket-1][G[now_position][i].first] = cost[now_ticket][now_position] + G[now_position][i].second/2;
                    que.push(pair<int,P>(cost[now_ticket-1][G[now_position][i].first],P(G[now_position][i].first,now_ticket-1)));
                }
            }
        }
    }
}

int main(){

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

        s--;
        d--;
        //cout << s << " " << d << endl;
        REP(i,ARRAY_MAX){//初期化
            G[i].clear();
        }

        REP(i,TICKET){//最短距離の初期化
            REP(j,ARRAY_MAX){
                cost[i][j] = INF;
                used[i][j] = false;
            }
        }

        REP(i,m){
            int a,b,f;
            cin >> a >> b >> f;
            a--;
            b--;
            G[a].push_back({b,f});
            G[b].push_back({a,f});
            //マップの作成
        }

        solve();

        int mini = INF;
        for(int i = 0;i <= c;i++){
            mini = min(mini,cost[i][d]);
        }
        cout << mini << endl;
    }


    return 0;
}