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 <vector>
#include <map>
#include <queue>
#include <algorithm>
using namespace std;

const int MAX_V = 101;
const int INF = 1e+8;

// 頂点は(ノード番号,割引券の数)の組
typedef pair<int,int> P;
// 状態は(コスト,頂点)の組
typedef pair<int,P> State;

struct edge{
	int to, cost;
	edge(int v, int cost_){
		to = v;
		cost = cost_;
	}
};

// 頂点数
int V;
// G[u][i] = ノード u に接続している i 番目の edge が返ってくる
vector<edge> G[MAX_V];

// 初期化
void init(int n){
	V = n;
	for(int i = 0 ; i < MAX_V ; i++ ){
		G[i].clear();
	}
}


// ノード番号 s を始点, 割引券の枚数を c としたダイクストラ法
int dijkstra(int s, int c, int g){
	// greater<State> を指定することで コスト が小さい順に取り出せる
	priority_queue<State, vector<State>, greater<State> > q;
	
	// d[c][v] := 割引券 c 枚でノード番号 v にたどり着く最小コスト
	int d[11][101];
	for(int i=0 ; i < 11 ; i++ ){
		for(int j=0 ; j < 101 ; j++ ){
			d[i][j] = INF;
		}
	}
	
	d[c][s] = 0;
	State start( 0 , P(s,c) );
	q.push( start );
	
	int result = INF;
	while( !q.empty() ){
		int now_cost = q.top().first;
		int v = q.top().second.first;
		int c =  q.top().second.second;
		q.pop();
		
		if( v == g ){
			result = now_cost;
			break;
		}
		
		if( d[c][v] < now_cost ) continue;
		
		for(int i=0 ; i < G[v].size() ; i++ ){
			edge e = G[v][i];
			
			int next_cost = d[c][v] + e.cost;
			if( next_cost < d[c][e.to] ){
				d[c][e.to] = next_cost;
				State next( next_cost , P(e.to,c) );
				q.push( next );
			}
			if( c > 0 ){
				next_cost = d[c][v] + e.cost/2 ;
				if( next_cost < d[c-1][e.to] ){
					d[c-1][e.to] = next_cost;
					State next( next_cost , P(e.to,c-1) );
					q.push( next );
				}
			}
		}
	}
	return result;
}

// 重み cost の辺 (u,v) の追加
void add_edge(int u, int v, int cost){
	edge e( v , cost );
	G[u].push_back( e );
	e.to = u;
	G[v].push_back( e );
}


int main(){
	int c,n,m,s,g;
	while( cin >> c >> n >> m >> s >> g, c || n || m || s || g ){
		init(n);
		s--; g--;
		for(int i=0 ; i < m ; i++ ){
			int u, v, cost;
			cin >> u >> v >> cost;
			u--; v--;
			add_edge(u,v,cost);
		}
		int ans = dijkstra( s , c , g );
		cout << ans << endl;
	}
}

C++: #include <stdio.h>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
typedef long long int ll;

using namespace std;

int minimum,num_ticket,num_town,m,start,goal,costTable[101][101];


struct Info{
    Info(){
        current_town = 0;
        index = 0;
    }
    bool visited[102];
    int current_town,index,costs[102],visited_town[101];

};

void func(Info info){

    int sum = 0,limit;

    if(info.current_town == goal || minimum != 2000000000)
    {

    	limit = min(num_ticket,info.index);

    	for(int i = 0; i < limit; i++){
    		sum += info.costs[i]/2;
    	}

    	for(int i = limit; i < info.index; i++){
    		sum += info.costs[i];
    	}

		if(info.current_town == goal){
			minimum = min(minimum,sum);
			return;
		}else{
			if(sum >= minimum){
				return;
			}
		}

    }

    int calc;
    for(int i = 1; i <= num_town; i++){
        if(costTable[info.current_town][i] != -1 && info.visited[i] == false){
            Info new_info;
            for(int k = 1; k <= num_town; k++)new_info.visited[k] = info.visited[k];
            new_info.visited[i] = true;
            new_info.current_town = i;

            if(costTable[info.current_town][i] > info.costs[0]){
            	new_info.costs[0] = costTable[info.current_town][i];
            	for(int k = 1; k <= info.index; k++){
            		new_info.costs[k] = info.costs[k-1];
            	}
            }else if(costTable[info.current_town][i] <= info.costs[info.index-1]){
            	for(int k = 0; k < info.index; k++){
            		new_info.costs[k] = info.costs[k];
            	}
            	new_info.costs[info.index] = costTable[info.current_town][i];
            }else{
            	for(calc = 0; info.costs[calc] >= costTable[info.current_town][i];calc++)new_info.costs[calc] = info.costs[calc];
				new_info.costs[calc] = costTable[info.current_town][i];
				calc++;
				for(;calc-1 < info.index;calc++)new_info.costs[calc] = info.costs[calc-1];
            }
            new_info.index = info.index+1;
            func(new_info);

        }
    }
}

int main(){

    int from,to,fee;

    while(true){
        scanf("%d %d %d %d %d",&num_ticket,&num_town,&m,&start,&goal);
        if(num_ticket == 0 && num_town == 0 && m == 0 && start == 0 && goal == 0)break;

        minimum = 2000000000;

        for(int i = 1; i <= num_town; i++){
            for(int k = 1; k <= num_town; k++)costTable[i][k] = -1;
        }

        for(int i = 0; i < m; i++){
            scanf("%d %d %d",&from,&to,&fee);
            costTable[from][to] = fee;
            costTable[to][from] = fee;
        }

        Info info;
        for(int i = 1; i <= num_town;i++)info.visited[i] = false;

        info.current_town = start;
        info.visited[start] = true;

        func(info);

        printf("%d\n",minimum);
    }


    return 0;
}