Dijkstra using pair

#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<algorithm>
#include<cstring>
#include<utility>
using namespace std;

#define mx 100002
#define  w first
#define  u second
#define  pb push_back
#define  mp make_pair

typedef  pair <int, int> pii;

vector<int>graph[mx],cost[mx];
long long dist[mx];
int parent[mx];

void dijkstra(int n)
{
    for(int i=0;i<=n;i++)
        parent[i]=dist[i]=-1;
    priority_queue<pii,vector<pii > ,greater<pii > >Q;
    Q.push(mp(0,1));
    dist[1]=0;
    while(!Q.empty())
    {
        pii top=Q.top();
        Q.pop();
        int u=top.u;
        for(int i=0; i<(int)graph[u].size(); i++)
        {
            int v=graph[u][i];
            if(dist[u]+cost[u][i]<dist[v]||dist[v]==-1)
            {
                dist[v]=dist[u]+cost[u][i];
                parent[v]=u;
                Q.push(mp(dist[v],v));
            }
        }
    }
}
int main()
{
    int n,e;
    scanf("%d%d",&n,&e);

    for(int i=0; i<e; i++)
    {
        int u,v,w;
        scanf("%d %d %d",&u,&v,&w);
        graph[u].push_back(v);
        graph[v].push_back(u);
        cost[u].push_back(w);
        cost[v].push_back(w);

    }
    dijkstra(n);
    return 0;
}