Go: // Warshall–Floyd Algorithm

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

var scanner = bufio.NewScanner(os.Stdin)

const INF = 2000000000

func main() {
	for scanner.Scan() {
		buf := strings.Split(scanner.Text(), " ")
		n, _ := strconv.Atoi(buf[0])
		m, _ := strconv.Atoi(buf[1])
		if n == 0 && m == 0 {
			break
		}
		c_matrix := make([][]int, m)
		for i := range c_matrix {
			c_matrix[i] = make([]int, m)
		}
		t_matrix := make([][]int, m)
		for i := range t_matrix {
			t_matrix[i] = make([]int, m)
		}
		for i := 0; i < n; i++ {
			scanner.Scan()
			buf_ := strings.Split(scanner.Text(), " ")
			a, _ := strconv.Atoi(buf_[0])
			b, _ := strconv.Atoi(buf_[1])
			c, _ := strconv.Atoi(buf_[2])
			t, _ := strconv.Atoi(buf_[3])
			c_matrix[a-1][b-1] = c
			t_matrix[a-1][b-1] = t
		}
		c_dist := make([][]int, m)
		c_prev := make([][]int, m)
		t_dist := make([][]int, m)
		t_prev := make([][]int, m)
		for i := 0; i < m; i++ {
			c_dist[i] = make([]int, m)
			c_prev[i] = make([]int, m)
			t_dist[i] = make([]int, m)
			t_prev[i] = make([]int, m)
		}
		for i := 0; i < m; i++ {
			for j := 0; j < m; j++ {
				if c_matrix[i][j] == 0 {
					c_dist[i][j] = INF
					c_prev[i][j] = -1
				} else {
					c_dist[i][j] = c_matrix[i][j]
					c_prev[i][j] = i
				}
				if t_matrix[i][j] == 0 {
					t_dist[i][j] = INF
					t_prev[i][j] = -1
				} else {
					t_dist[i][j] = t_matrix[i][j]
					t_prev[i][j] = i
				}
			}
			c_dist[i][i] = 0
			t_dist[i][i] = 0
		}
		for k := 0; k < m; k++ {
			for i := 0; i < m; i++ {
				for j := 0; j < m; j++ {
					c_newlen := c_dist[i][k] + c_dist[k][j]
					if c_newlen < c_dist[i][j] {
						c_dist[i][j] = c_newlen
						c_prev[i][j] = c_prev[k][j]
					}
				}
			}
		}
		for k := 0; k < m; k++ {
			for i := 0; i < m; i++ {
				for j := 0; j < m; j++ {
					t_newlen := t_dist[i][k] + t_dist[k][j]
					if t_newlen < t_dist[i][j] {
						t_dist[i][j] = t_newlen
						t_prev[i][j] = t_prev[k][j]
					}

				}
			}
		}
		scanner.Scan()
		k, _ := strconv.Atoi(scanner.Text())
		for i := 0; i < k; i++ {
			scanner.Scan()
			buf_ := strings.Split(scanner.Text(), " ")
			p, _ := strconv.Atoi(buf_[0])
			q, _ := strconv.Atoi(buf_[1])
			r, _ := strconv.Atoi(buf_[2])
			switch r {
			case 0:
				fmt.Println(c_dist[p-1][q-1])
			case 1:
				fmt.Println(t_dist[p-1][q-1])
			}
		}
	}
}

C++: #define INF 100000;

#include<iostream>
#include<vector>
using namespace std;

struct Node{
  int num;

  vector<int> edge_to;
  vector<int> edge_cost;
  vector<int> edge_time;

  bool done;
  int cost;
  int time;
};

int main(){
  for(;;){
    int n,m,a,b,c,t,p,q,r;
    cin>>n>>m;
    if(n==0&&m==0)break;
    vector<Node> node;

    Node no;

    for(int i=1;i<=m;i++){
      no.num=i;
      no.done=false;
      no.cost=-1;
      no.time=-1;
      node.push_back(no);
    }


    while(n--){
      cin>>a>>b>>c>>t;
      node[a-1].edge_to.push_back(b);
      node[b-1].edge_to.push_back(a);
      node[a-1].edge_cost.push_back(c);
      node[b-1].edge_cost.push_back(c);
      node[a-1].edge_time.push_back(t);
      node[b-1].edge_time.push_back(t);
    }

    cin>>n;
    while(n--){
      cin>>p>>q>>r;

      vector<Node> n(node.size());
      copy(node.begin(),node.end(),n.begin());
      p--;
      q--;

      if(r){

	n[p].time = 0;
	while(1){

	  int d=-1;

	  for(int i=0;i<n.size();++i){
	    if( n[i].done || n[i].time < 0) {
	      continue;
	    } else if(!(d != -1) && !(n[i].time >= n[d].time)) {
	      d=i;
	    }
	  }

	  if ( d == -1 )
	    break;

	  n[d].done = true;

	  for(int i=0;i<n[d].edge_to.size();++i) {
	    int ttime = n[d].time + n[d].edge_time[i];
	    if(n[n[d].edge_to[i]-1].time < 0 || ttime < n[n[d].edge_to[i]-1].time){
	      n[n[d].edge_to[i]-1].time = ttime;
	    }
	  }

	}
	cout<<n[q].time<<endl;

      }else{

	n[p].cost = 0;
	while(1){

	  int d=-1;

	  for(int i=0;i<n.size();++i){
	    if( n[i].done || n[i].cost < 0) {
	      continue;
	    } else if(!(d != -1) && !(n[i].cost < n[d].cost)) {
	      d=i;
	    }
	  }

	  if ( d == -1 )
	    break;

	  n[d].done = true;

	  for(int i=0;i<n[d].edge_to.size();++i) {
	    int tcost= n[d].cost + n[d].edge_cost[i];
	    if(n[n[d].edge_to[i]-1].cost < 0 || tcost < n[n[d].edge_to[i]-1].cost){
	      n[n[d].edge_to[i]-1].cost = tcost;
	    }
	  }

	}
	cout<<n[q].cost<<endl;

      }

    }
  }
}

C++: #include <iostream>
#include <algorithm>
#include <cassert>
#include <cctype>
#include <complex>
#include <cstdio>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;

#define INF 1e9
#define rep(i,n) for(int i=0;i<n;i++)
struct edge{int to,cost,time;};
typedef pair<int,int> P;

int V,E,d[1001],a,b,c,t,S,G,k,r;
edge e;
vector<edge> g[1001];

int main(){
	while(cin>>E>>V&&V){
		rep(i,V+1)g[i].clear();
		rep(i,E){
			cin>>a>>b>>c>>t;
			e.to=b;e.cost=c;e.time=t;
			g[a].push_back(e);
			e.to=a;
			g[b].push_back(e);
		}
		cin>>k;
		rep(h,k){
		cin>>S>>G>>r;
		priority_queue<P,vector<P>,greater<P> > q;
		fill(d,d+V+1,INF);
		d[S]=0;
		q.push(P(0,S));
		while(!q.empty()){
			P p=q.top();q.pop();
			int v=p.second;
			if(d[v]<p.first)continue;
			rep(i,g[v].size()){
				e=g[v][i];
				if(!r)if(d[e.to]>d[v]+e.cost){
					d[e.to]=d[v]+e.cost;
					q.push(P(d[e.to],e.to));
				}
				if(r)if(d[e.to]>d[v]+e.time){
					d[e.to]=d[v]+e.time;
					q.push(P(d[e.to],e.to));
				}
			}
		}
		if(d[G]<INF)cout<<d[G]<<endl;
		else cout<<"unreachable"<<endl;
		}
	}
}