Go: package main

import (
	"container/heap"
	"fmt"
	"runtime"
)

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]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)
					}
				}
			}
		}
		runtime.GC()
	}
}

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]; for(int i=0;i<111;i++)for(int j=0;j<11;j++) dist[i][j] = INF;
  priority_queue < PP, vector<PP>, greater<PP> > que;
 
  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;
 
    //if(dist[now][tic] < cost) continue;
    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][i]); } //cout << ans << endl; }
  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;
  }
   
}

C++: #include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <string>
#include <cstring>
#include <complex>
#include <ctime>
#include <cstdlib>

using namespace std;

inline int to_int(string s) {int v; istringstream sin(s); sin >> v; return v;}
template<class T> inline string to_str(T x) {ostringstream sout; sout << x; return sout.str();}

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

const int INF = 1 << 30;
const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};

int n, m, res;

#define debug(a, b, c) for(int i = 0; i < b; i++){for(int j = 0; j < c; j++){printf("%12d", a[i][j]);}puts("");}puts("-----------------------------------------");

int main()
{
	int wk, tk, c;
	int disc, city, line, start, goal;
	int route[512][512], cost[512][16];
	bool used[512];
	while(cin >> disc >> city >> line >> start >> goal)
	{
		if(!disc && !city && !line && !start && !goal) break;

		start--, goal--;
		for(int i = 0; i < city; i++)
		{
			fill(route[i], route[i] + city, INF);
			fill(cost[i], cost[i] + city, INF);
		}

		for(int i = 0; i < line; i++)
		{
			cin >> wk >> tk >> c;
			route[wk-1][tk-1] = c;
			route[tk-1][wk-1] = c;
		}

		for(int m = 0; m <= disc; m++)
		{
			cost[start][m] = 0;
			//debug(cost, disc, city);
			fill(used, used + city, false);

			while(true)
			{
				int v = -1;
				for(int i = 0; i < city; i++)
				{
					if(!used[i] && (v == -1 || cost[i][m] < cost[v][m])) v = i;
				}

				if(v == -1) break;

				used[v] = true;

				for(int i = 0; i < city; i++)
				{
					if(m == 0)	
						cost[i][m] = min(cost[i][m], cost[v][m] + route[v][i]);
					else
						cost[i][m] = min(cost[v][m - 1] + route[v][i] / 2, min(cost[i][m], cost[v][m] + route[v][i]));
				}
			}
		}
		cout <<	cost[goal][disc] << endl;

	}
}

C++: #include <iostream>
#include <vector>
#include <queue>
using namespace std;

#define INF 100000000

struct edge {
	int to;
	int f;
	edge(int to_, int f_) {
		to = to_; f = f_;
	}
	edge(){}
};
struct status {
	int vertex;
	int cost;
	int c;
	status(int vertex_, int cost_, int c_) {
		vertex = vertex_; cost = cost_; c = c_;
	}
	status(){}
	bool operator<(const status & obj) const {
		if(this->c != obj.c)
			return this->c < obj.c;
		return this->cost > obj.cost;
	}
};

int main() {
	while(true) {
		int c, n, m, s, d;
		cin >> c >> n >> m >> s >> d;
		if(!(c || n || m || s || d))
			break;
		s--; d--;
		vector<vector<edge> > v(n);
		for(int i = 0; i < m; i++) {
			int a, b, f;
			cin >> a >> b >> f;
			a--; b--;
			v[a].push_back(edge(b,f));
			v[b].push_back(edge(a,f));
		}
		priority_queue<status> q;
		int cost[128][16];
		for(int i = 0; i < 128; i++)
			for(int j = 0; j < 16; j++)
				cost[i][j] = INF;
		q.push(status(s, 0, c));
		while(!q.empty()) {
			status cur;
			cur = q.top(); q.pop();

			if(cost[cur.vertex][cur.c] == INF) {
				cost[cur.vertex][cur.c] = cur.cost;
				for(int i = 0; i < v[cur.vertex].size(); i++) {
					if(cost[v[cur.vertex][i].to][cur.c] == INF) {
						q.push(status(v[cur.vertex][i].to, v[cur.vertex][i].f + cur.cost, cur.c));
					}
					if(cur.c > 0 && cost[v[cur.vertex][i].to][cur.c-1] == INF) {
						q.push(status(v[cur.vertex][i].to, v[cur.vertex][i].f / 2 + cur.cost, cur.c - 1));
					}
				}
			}
		}

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