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)
		}
		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)
		start := Node{NowPosition: s, DiscountTicketTCount: c, Amount: 0}
		heap.Push(&pq, &start)
		memo := make(map[Memo]struct{})
		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}] = struct{}{}
			for _, v := range pointMap[now.NowPosition] {
				next := &Node{v.NextPoint, now.DiscountTicketTCount, now.Amount + v.Fee}
				if _, ok := memo[Memo{NowPoint: v.NextPoint, DiscountTicketTCount: now.DiscountTicketTCount}]; !ok {
					heap.Push(&pq, next)
				}
				if now.DiscountTicketTCount > 0 {
					next = &Node{v.NextPoint, now.DiscountTicketTCount - 1, now.Amount + v.Fee/2}
					if _, ok := memo[Memo{NowPoint: v.NextPoint, DiscountTicketTCount: now.DiscountTicketTCount}]; !ok {
						heap.Push(&pq, next)
					}
				}
			}
		}
	}
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#define INF 1000000000;
#define dis first
#define mati second.first
#define sta  second.second
using namespace std;
typedef pair <int ,pair <int,int> > P;
vector <P> mp[101];
int c,n,m,start,goal;

int bit_count(int a) {
  a = (a & 0x55555555)+((a & 0xAAAAAAAA) >> 1 );
  a = (a & 0x33333333)+((a & 0xCCCCCCCC) >> 2 );
  a = (a & 0x0F0F0F0F)+((a & 0xF0F0F0F0) >> 4 );
  a = (a & 0x00FF00FF)+((a & 0xFF00FF00) >> 8 );
  a = (a & 0x0000FFFF)+((a & 0xFFFF0000) >> 16);
  return a;
}

void henkan(int n,int kai) {
  if(kai <= 10) {
    henkan(n/2,kai+1);  
  cout << n % 2 ;
  if(kai == 0) cout << endl;
  }
}

int dijkstra() {
  int flg[1025][102] = {},dis[1025][102];
  for(int j=0;j<1<<n;j++)
    for(int i=0;i<=n;i++) dis[j][i] = -INF;

  for(int j=1;j<1<<n;j++)flg[j][start] = 1;

  priority_queue <P> Q;
  P t;
  t.dis = 0, t.mati = start, t.sta = 0;
  Q.push(t);

  while(!Q.empty()) {
    t = Q.top(),Q.pop();
    if(flg[t.sta][t.mati] == 1) continue;
    flg[t.sta][t.mati] = 1;
    for(int i=0;i<mp[t.mati].size();i++){
      int ndis = mp[t.mati][i].dis;
      int nmati = mp[t.mati][i].mati;
      int nsta = t.sta | (1<<(nmati-1));
      P tt;
      if(dis[t.sta][nmati] < t.dis-ndis && flg[t.sta][nmati] == 0) {
	tt.dis = t.dis-ndis,tt.mati = nmati,tt.sta = t.sta;
	dis[t.sta][nmati] = t.dis-ndis;
	Q.push(tt);
      }
      if(bit_count(nsta)<= c&&dis[nsta][nmati]<t.dis-ndis/2 && flg[nsta][nmati]==0){
	tt.dis = t.dis - ndis/2 , tt.mati = nmati, tt.sta = nsta;
	dis[nsta][nmati] = t.dis-ndis/2;
	Q.push(tt);
      }
    }
  }

  int ans = -INF;
  for(int j=0;j<1<<n;j++)ans = max(ans,dis[j][goal]);
   
  return -ans;
}


int main() {

  while(1) {
    cin >> c >> n >> m >> start >> goal;
    if(c==0&&n==0&&m==0&&start==0&&goal==0) break;

    for(int i=0;i<=n;i++) mp[i].clear();
    for(int i=0;i<m;i++) {
      int a,b,f;
      cin >> a >> b >> f;
      P t;
      t.dis = f,  t.mati = b , t.sta = 0;
      mp[a].push_back(t);
      t.mati = a;
      mp[b].push_back(t);
    }

    cout << dijkstra() << endl;
  }

  return 0;
}

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

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,j) FOR(i,0,j)

const int INF = 1 << 24;
const int dx[4] = {0, 0, 1, -1}, dy[4] = {1, -1, 0, 0};

typedef unsigned long long ull;

struct Edge{
    int to, cost;
};

int C, N, M, S, D;
int cost[110][110];
int d[110][20], used[110][20];

void dijkstra(){
    REP(i, 110){
        REP(j, 20){
            d[i][j] = INF;
            used[i][j] = 0;
        }
    }

    d[S][0] = 0;

    while(1){
        int u = -1, v = -1;
        REP(i, N){
            REP(j, C){
                if(!used[i][j] && (u == -1 || d[u][v] > d[i][j])){u = i; v = j;}
            }
        }

        if(u == -1){break;}
        used[u][v] = 1;

        REP(i, N){
            d[i][v+1] = std::min(d[i][v+1], d[u][v] + cost[u][i] / 2);
            d[i][v] = std::min(d[i][v], d[u][v] + cost[u][i]);
        }
    }
}

int main(){
    while(std::cin >> C >> N >> M >> S >> D, C){
        S--; D--;

        REP(i, 110){
            REP(j, 110){
                cost[i][j] = INF;
            }
        }

        REP(i, M){
            int from, to, co;
            std::cin >> from >> to >> co;
            from--; to--;
        
            cost[from][to] = co;
            cost[to][from] = co;
        }

        dijkstra();

        int res = INF;
        REP(i, C+1){
            res = std::min(res, d[D][i]);
        }

        std::cout << res << std::endl;
    }
}

C++: #include<bits/stdc++.h>
using namespace std;

struct Node{
    int townNum, fare, ticketNum;
    bool operator<(const Node &obj)const{
        if(fare != obj.fare)return fare > obj.fare;
        return false;
    }
};

int mini[100][11];

int main(){
    while(1){
        int c,n,m,s,d;
        scanf("%d %d %d %d %d",&c,&n,&m,&s,&d);
        if(c == 0 && n == 0 && m == 0 && s == 0 && d == 0)break;
        vector< vector<Node> > graph;
        graph.resize(n+1);

        for(int i=0;i<m;++i){
            int a,b,f;
            scanf("%d %d %d",&a,&b,&f);
            graph[a].push_back((Node){b,f,0});
            graph[b].push_back((Node){a,f,0});
        }

        for(int i=0;i<n;++i){
            for(int j=0;j<=c;++j){
                mini[i][j] = INT_MAX;
            }
        }
        mini[s-1][c] = 0;

        priority_queue<Node> Q;
        Q.push((Node){s,0,c});
        while(!Q.empty()){
            Node now = Q.top();
            Q.pop();
            if(now.townNum == d){
                cout << now.fare << endl;
                break;
            }
            for(int i=0;i<graph[now.townNum].size();++i){
                Node nextTown = graph[now.townNum][i];
                int newfare=now.fare+nextTown.fare;
                if(newfare < mini[nextTown.townNum-1][now.ticketNum]){
                    Q.push((Node){nextTown.townNum,newfare,now.ticketNum});
                    mini[nextTown.townNum-1][now.ticketNum] = newfare;
                }
                if(now.ticketNum > 0){
                    newfare = now.fare + nextTown.fare / 2;
                    if(newfare < mini[nextTown.townNum-1][now.ticketNum-1]){
                        Q.push((Node){nextTown.townNum,newfare,now.ticketNum-1});
                        mini[nextTown.townNum-1][now.ticketNum-1] = newfare;
                    }
                }
            }
        }
    }

    return 0;
}