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
}

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)
		for len(pq) != 0 {
			now := heap.Pop(&pq).(*Node)
			if now.NowPosition == d {
				fmt.Println(now.Amount)
				break
			}
			for _, v := range pointMap[now.NowPosition] {
				next := &Node{v.NextPoint, now.DiscountTicketTCount, now.Amount + v.Fee}
				heap.Push(&pq, next)
				if now.DiscountTicketTCount > 0 {
					next = &Node{v.NextPoint, now.DiscountTicketTCount - 1, now.Amount + v.Fee/2}
					heap.Push(&pq, next)
				}
			}
		}
	}
}

C++: #include<iostream>
#include<algorithm>

const int INF = 1 << 24;
int ticket, V, E, start, goal;
//d[i][j]: i枚使ったんだよー
int d[11][101], used[11][101], cost[101][101];

int dijkstra(int s){
	for(int i=0;i<11;i++){
		std::fill(d[i], d[i]+101, INF);
		std::fill(used[i], used[i]+101, 0);
	}

	d[0][s] = 0;

	while(true){
		int u = -1, v;
		for(int i=0;i<=ticket;i++){
			for(int j=1;j<=V;j++){
				if(!used[i][j] && (u == -1 || d[i][j] < d[u][v])){
					u = i;
					v = j;
				}
			}
		}

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

		for(int j=1;j<=V;j++){
			d[u][j] = std::min(d[u][j], d[u][v] + cost[v][j]);
			if(u+1 <= ticket){
				d[u+1][j] = std::min(d[u+1][j], d[u][v] + cost[v][j] / 2);
			}
		}
	}
	
}

int main(){
	while(std::cin >> ticket >> V >> E >> start >> goal, V){
		for(int i=1;i<=100;i++){
			for(int j=1;j<=100;j++){
				cost[i][j] = INF;
			}
		}
		for(int i=0;i<E;i++){
			int a, b, f;
			std::cin >> a >> b >> f;
			cost[a][b] = cost[b][a] = f;
		}
		dijkstra(start);
		int res = INF;
		for(int i=0;i<=ticket;i++){
			res = std::min(res, d[i][goal]);
		}
		std::cout << res << std::endl;
	}
}

C++: #include<iostream>
#include<queue>
#include<string.h>
using namespace std;

const int INF = 1<<30;

struct Node{
  int use,to,weight;
  Node() {;}
  Node(int use,int to,int weight) : use(use), to(to), weight(weight) {;}
};
bool operator<(const Node &e,const Node &f) {
  return e.weight > f.weight;
}

int dist[110][110];
bool visit[110];
int dist2[110][110];

int main() {
  int c,n,m,s,d,a,b,f;
    while(cin>>c>>n>>m>>s>>d, c|n|m|s|d) {
      s--,d--;

      for(int i=0; i<110; ++i) {
	for(int j=0; j<110; ++j) {
	  dist[i][j] = INF;
	}
	visit[i] = false;
      }

      for(int i=0; i<110; ++i)
	for(int j=0; j<110; ++j)
	  dist2[i][j] = INF;

      for(int i=0; i<m; ++i) {
	cin>>a>>b>>f;
	a--,b--;
	dist[a][b] = f;
      }

      priority_queue<Node> Q;
      Q.push(Node(0,s,0));
      visit[s] = true;
      while(!Q.empty()) {
	Node now = Q.top(); Q.pop();

	if(now.to == d) {
	  cout<<now.weight<<endl;
	  break;
	}

	visit[now.to] = true;
	for(int i=0; i<n; ++i) {
	  if(!visit[i] && dist[now.to][i] != INF) {
	    if(dist2[now.use+1][i]
	       > now.weight + dist[now.to][i]/2 && now.use < c) {
	      dist2[now.use+1][i] = now.weight + dist[now.to][i]/2;
	      Q.push(Node(now.use+1, i, dist2[now.use+1][i]));
	    }
	    if(dist2[now.use][i]
	       > now.weight + dist[now.to][i]) {
	      dist2[now.use][i] = now.weight + dist[now.to][i];
	      Q.push(Node(now.use, i, dist2[now.use][i]));
	    }
	  }
	}
      }

/*
      for(int i=0; i<=c; ++i) {
	cout<<dist2[i][d]<<" : "<<i<<endl;
      }
*/
    }
}

C++: #include<iostream>
#include<iomanip>
#include<algorithm>
#include<vector>
#include<map>
#include<queue>
#define fr first
#define sc second
using namespace std;
#define INF 10000000
typedef pair<int,int> iiP;
typedef pair<int,iiP> P;
struct edge{
  int to,cost;
  edge(){}
  edge(int to,int cost):to(to),cost(cost){};
};
int c,n,m;
int S,G;
int min_cost[101][10];
bool used[101][10];
vector< vector<edge> > info;
int solve();
int main(){
  while(cin >> c >> n >> m >> S >> G && (c||n||m||S||G)){
  for(int i=0;i<101;i++){
    for(int j=0;j<10;j++){
      min_cost[i][j] = INF;
      used[i][j] = false;
    }
  }
  info.resize(n + 1);
  for(int i=0,a,b,f;i<m;i++){
    cin >> a >> b >> f;
    info[a].push_back(edge(b,f));
    info[b].push_back(edge(a,f));
  }
  cout << solve() << endl;

  for(int i=0;i<=n;i++) info[i].clear();
  }
}
int solve(){
  priority_queue< P,vector<P>,greater<P> > que;

  min_cost[S][c] = 0;
  que.push(P(0,iiP(S,c)));

  while(!que.empty()){
    P p = que.top();
    int cost = p.fr,now = p.sc.fr,KEN = p.sc.sc;
    que.pop();

    if( now == G) return cost;

    if( used[now][KEN] ) continue;
    used[now][KEN] = true;

    for(int i = 0,l = info[now].size();i < l;i++){
      edge e = info[now][i];
      if(cost + e.cost < min_cost[e.to][KEN]){
        min_cost[e.to][KEN] = cost + e.cost;
        que.push(P(min_cost[e.to][KEN],iiP(e.to,KEN)));
      }
      if(KEN != 0){
        if( cost + e.cost/2 < min_cost[e.to][KEN-1] ){
          min_cost[e.to][KEN-1] = cost + e.cost/2;
          que.push(P(min_cost[e.to][KEN-1],iiP(e.to,KEN-1)));
        }
      }
    }
  }
}

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][20]={};
		int ans =0;
		priority_queue < PP, vector<PP>, greater<PP> > q;
		vector< P > way[110];
		for(int i=0;i<m;i++)
		{
			int a,b,f;
			cin>>a>>b>>f;
			way[a].push_back(P(b,f));
			way[b].push_back(P(a,f));
		}
		PP next;
		q.push(PP(0,P(s,c)));
		while(!q.empty())
		{
			PP now=q.top();q.pop();
			
			flg[now.second.first][now.second.second]=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][now.second.second]!=1){
				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;
				if(flg[way[now.second.first][i].first][now.second.second-1]!=1){
				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;
}