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 <queue>
using namespace std;

struct State {
    int no_;
    int cost_;
    int ticket_;
    State(int no, int cost, int ticket) 
        : no_(no), cost_(cost), ticket_(ticket) {} 
    
};

struct Edge {
    int to_;
    int cost_;
    Edge(int to, int cost) 
        : to_(to), cost_(cost) {}
};

int c, n, m, s, d;

auto dijkstra(vector<vector<Edge>> &g, vector<vector<int>> &dm) -> int {
    auto comp = [](auto& lhs, auto& rhs){return lhs.cost_ > rhs.cost_;};
    priority_queue<State, vector<State>, decltype(comp)> que(comp);

    que.push(State(s, 0, c));
    for (auto &e : dm[s]) {
        e = 0;
    }
    while (!que.empty()) {
        State s = que.top();
        que.pop();
        int current_no = s.no_;
        int current_cost = s.cost_;
        int current_ticket = s.ticket_;
        for (auto &e : g[current_no]) {
            int to = e.to_;
            int cost = e.cost_;
            if (current_ticket > 0) {
                // not use ticket
                if (dm[to][current_ticket] > dm[current_no][current_ticket] + cost) {
                    que.push(State(to, dm[current_no][current_ticket] + cost, current_ticket));
                    dm[to][current_ticket] = dm[current_no][current_ticket] + cost;
                }
                // use ticket
                if (dm[to][current_ticket-1] > dm[current_no][current_ticket] + cost/2) {
                    que.push(State(to, dm[current_no][current_ticket] + cost/2, current_ticket-1));
                    dm[to][current_ticket-1] = dm[current_no][current_ticket] + cost/2;
                }
            }else {
                if (dm[to][current_ticket] > dm[current_no][current_ticket] + cost) {
                    que.push(State(to, dm[current_no][current_ticket] + cost, current_ticket));
                    dm[to][current_ticket] = dm[current_no][current_ticket] + cost;
                }
            }
        }
    }

    int ans = 1e8;
    for (auto &e : dm[d]) {
        ans = min(ans, e);
    }
    return ans;
}

auto main(int argc, char const *argv[]) -> int {
    constexpr int INF = 1e8;

    while(cin>>c>>n>>m>>s>>d, c||n||m||s||d) {
        vector<vector<Edge>> g(n+1);
        vector<vector<int>> dm(n+1);
        for (auto &e : dm) {
            for (int i = 0; i < c + 1; ++i) {
                e.push_back(INF);
            }
        }

        for (int i = 0; i < m; ++i) {
            int a, b, f;
            cin>>a>>b>>f;
            g[a].push_back(Edge(b, f));
            g[b].push_back(Edge(a, f));
        }
        cout<<dijkstra(g, dm)<<endl;
    }
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>
#include <string>
#include <bitset>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <string.h>

#define X first
#define Y second
#define MP make_pair
typedef long long ll;
using namespace std;

int mindis[110], pre[110];
bool used[110];
int eCost[110][110];

int getPathSum(int c, int p, int g){
	vector<int> edge;
	edge.push_back(eCost[p][g]);
		
	int to = p;
	for(int from = pre[to]; from != 0; from = pre[from]){
		edge.push_back(eCost[from][to]);
		to = from;
	}

	sort(edge.begin(), edge.end());

	int idx = edge.size()-1;
	for(int i = 0; i < c; i++){
		edge[idx--] /= 2;
		if(idx < 0) break;
	}
	
	int ans = 0;
	for(int i = 0; i < edge.size(); i++){
		ans += edge[i];
	}

	return ans;
}

int main(){
	int c, n, m, s, d;
	while(cin >> c >> n >> m >> s >> d){
		if(c == 0 && n == 0 && m == 0 && s == 0 && d == 0) break;

		fill(mindis, mindis+110, 1<<30);
		fill(pre, pre+110, 0);
		fill(used, used+110, false);
		for(int i = 0; i < 110; i++) fill(eCost[i], eCost[i]+110, 1<<30);

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

		mindis[s] = 0;
		vector<int> goals;

		//最短経路(ダイクストラ)
		while(true){
			int v = -1;
			for(int i = 1; i <= n; i++){
				if(!used[i] && (v == -1 || mindis[v] > mindis[i])) v = i;
			}

			if(v == d) break;
			used[v] = true;

			for(int i = 1; i <= n; i++){
				if(mindis[i] > mindis[v]+eCost[v][i]){
					if(i == d){
						//次がゴールならここでチケットを適用した総和を出して最終的な結果にする
						//それをgoalsに格納していく
						goals.push_back(getPathSum(c, v, i));
					}else{
						mindis[i] = mindis[v]+eCost[v][i];
						pre[i] = v;
					}
				}
			}
		}

		int minc = 100000000;
		for(int i = 0; i < goals.size(); i++){
			if(minc > goals[i]) minc = goals[i];
		}

		cout << minc << endl;
	}
	return 0;
}