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 <vector>
#include <queue>
#include <map>
#include <cassert>
#include <algorithm>
using namespace std;
typedef pair<int, int> edge;
struct state{
  int cost, coupon, station;
  state(int cost_, int coupon_, int station_):cost(cost_), coupon(coupon_), station(station_){}
  bool operator> (const state &s) const{
    if(cost == s.cost){
      return coupon < s.coupon;
    }
    return cost > s.cost;
  }
};
int djikstra(vector<vector<edge> > graph, int start, int goal, int coupon){
  priority_queue<state, vector<state>, greater<state> > pq;
  pq.push(state(0, coupon, start));
  bool visited[coupon][graph.size()];
  fill_n((bool*)visited, (coupon+1) * graph.size(), false);
  while(!pq.empty()){
    state cur = pq.top(); pq.pop();
    if(visited[cur.coupon][cur.station]){
      continue;
    }
    if(cur.station == goal){
      return cur.cost;
    }
    visited[cur.coupon][cur.station] = true;
    for(int i = 0; i < graph[cur.station].size(); ++i){
      int to = graph[cur.station][i].first;
      int c = graph[cur.station][i].second;
      if(cur.coupon > 0){
        pq.push(state(cur.cost+c/2, cur.coupon-1, to));
      }
      pq.push(state(cur.cost+c, cur.coupon, to));
    }
  }
  assert(false);
}
int main(){
  int c, n, m, s, d;
  while(true){
    cin >> c >> n >> m >> s >> d;
    if((c|n|m|s|d) == 0){
      break;
    }
    vector<vector<edge> > graph(n+1, vector<edge>());
    for(int i = 0; i < m; ++i){
      int a, b, f;
      cin >> a >> b >> f;
      graph[a].push_back(make_pair(b, f));
      graph[b].push_back(make_pair(a, f));
    }
    cout << djikstra(graph, s, d, c) << endl;
  }
  return 0;
}

C++: #include <map>
#include <vector>
#include <cstdio>
using namespace std;
int cost[101][11];
int main(){
	int c,N,m,s,d,i,j,k,x;
	for(;scanf("%d%d%d%d%d",&c,&N,&m,&s,&d),N;){
		vector<map<int,int> >dist(N+1);
		memset(cost,99,sizeof(cost));
		for(k=0;k<m;k++){
			scanf("%d%d%d",&i,&j,&x);dist[i][j]=dist[j][i]=x;
		}
		for(i=0;i<=c;i++)cost[s][i]=0;
		for(;~c;c--){
			vector<bool>used(N+1);
			for(;;){ //dijkstra
				int m=9999999;
				for(i=0;i<N;i++)if(!used[i]&&m>cost[i][c])m=cost[i][c];
				if(m==9999999)break;
				for(j=0;j<N;j++)if(m==cost[j][c]){
					map<int,int>::iterator it=dist[j].begin();
					for(used[j]=1;it!=dist[j].end();it++){
						if(cost[it->first][c]>it->second+cost[j][c])cost[it->first][c]=it->second+cost[j][c];
						if(c&&cost[it->first][c-1]>it->second/2+cost[j][c])cost[it->first][c-1]=it->second/2+cost[j][c];
					}
				}
			}
		}
		printf("%d\n",cost[d][0]);
	}
}

C++: #include<iostream>
#include<string>
#include<vector>
#include<cstdio>
#include<queue>
#include<map>
#define P pair<int,int>
using namespace std;

struct K {
	int basho, nokori, mincost;
};
bool operator<(K a, K b) {
	return a.mincost > b.mincost;
}
int main() {
	int cost[100][11];//n???????????°????????§m????????????????°????
	int B, c, d, e, f;
	while (scanf("%d%d%d%d%d", &B, &c, &d, &e, &f), B || c || d || e || f) {
		vector<P>a[100]{};
		memset(cost, 0x3f, sizeof(cost));
		e--; f--; cost[e][B] = 0;
		priority_queue<K>Q;
		K g;
		g.basho = e; g.nokori = B; g.mincost = 0;
		Q.push(g);
		for (int h = 0; h < d; h++) {
			int i, j, k;
			scanf("%d%d%d", &i, &j, &k);
			i--; j--;
			a[i].push_back(P(k, j));
			a[j].push_back(P(k, i));
		}
		while (Q.size()) {
			K l = Q.top(); Q.pop();
			int m = l.mincost, n = l.nokori, b = l.basho;
			if (cost[b][n] < m)continue;
			for (P o : a[b]) {
				if (cost[o.second][n] > cost[b][n] + o.first) {
					cost[o.second][n] = cost[b][n] + o.first;
					K xx;
					xx.basho = o.second;
					xx.mincost = cost[o.second][n];
					xx.nokori = n;
					Q.push(xx);
				}
				if (n&&cost[o.second][n-1] > cost[b][n] + o.first / 2) {
					cost[o.second][n - 1] = cost[b][n] + o.first / 2;
					K yy;
					yy.basho = o.second;
					yy.nokori = n - 1;
					yy.mincost = cost[o.second][n - 1];
					Q.push(yy);
				}
			}
		}
		int MINCOST = 1 << 29;
		for (int sss = 0; sss < 11; sss++) {
			MINCOST = min(MINCOST, cost[f][sss]);
		}
		cout << MINCOST << endl;
	}
}

C++: #include<bits/stdc++.h>
#define F first
#define S second
#define INF 1<<28
using namespace std;

int c, n, s, d;
typedef pair < int, int > P;
typedef pair < int, P > PP;
vector < P > vec[111];

int solve(){
  
  int dist[111][11]; 
  priority_queue < PP, vector<PP>, greater<PP> > que;
  
  for(int i=0;i<111;i++) for(int j=0;j<11;j++) dist[i][j] = INF;
  dist[s][c] = 0;
  que.push( PP(0, P(s, c)) ); //Now_cost, Now_node, Now_ticket
  
  while(!que.empty()){
    PP p = que.top(); que.pop();
    int cost = p.F, now = p.S.F, tic = p.S.S;
    
    for(int i=0;i<vec[now].size();i++){
      P to = vec[now][i];
      if(dist[to.S][tic] > cost + to.F){
	dist[to.S][tic] = cost + to.F;
	que.push( PP(dist[to.S][tic], P(to.S, tic)) );
      }
      if(tic && dist[to.S][tic-1] > cost + to.F/2){
	dist[to.S][tic-1] = cost + to.F/2;
	que.push( PP(dist[to.S][tic-1], P(to.S, tic-1)) );
      }
    }
  }

  int ans = INF;
  for(int i=0;i<=c;i++) ans = min(ans, dist[d][0]);
  return ans;
}

int main(){

  int m, a, b, p;
  
  while(cin >> c >> n >> m >> s >> d){
    if((c|n|m|s|d) == 0) break;
    for(int i=0;i<111;i++) vec[i].clear();
    for(;m--;){
      cin >> a >> b >> p;
      vec[a].push_back(P(p, b)); //[now] P(cost, next);
      vec[b].push_back(P(p, a));
    }
    
    cout << solve() << endl;
  }
  
}