0x3f -> 0x3f3f3f3f

#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
const int N = 510;
int g[N][N];
int d[N];
bool st[N];
int n, m;

int Dijkstra()
{
    memset(d,0x3f,sizeof d);
    d[1] = 0;
    for(int i = 0;i < n;i++)
    {
        int u = -1;
        for(int j = 1; j<= n;j++)
        {
            if(((u == -1) || d[j] < d[u]) && !st[j])
            {
                u = j;
            }
        }
        st[u] = true;

        for(int k = 1; k <= n;k++)
        {
            d[k] = min(g[u][k] + d[u],d[k]);
        }

    }
    if(d[n]==0x3f3f3f3f) return -1;  //如果第n个点路径为无穷大即不存在最低路径
    return d[n];
}
int main()
{
    memset(g,0x3f,sizeof g);
    cin >> n >> m;
    int a, b, c;
    for(int i = 0;i < m;i++)
    {
        cin >> a>> b>> c;
        g[a][b] = min(g[a][b],c);
    }

    cout << Dijkstra();

    return 0;
}