Dijkstra模板 (n^2)

#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdio>
#include<string.h>
#include<limits.h>
#include<vector>
#define INF 0x3f3f3f3f
using namespace std;
const int maxn = 505;
int a[maxn][maxn],vis[maxn],dist[maxn];
int n,m;
int main(void) {
    void dijkstra();
    memset(a,0x3f,sizeof(a));
    memset(dist,0x3f,sizeof(dist));          // 刚开始每个顶点之间的距离都设置为无穷大
    memset(vis,0,sizeof(vis));
    scanf("%d%d",&n,&m);
    int x,y,w;
    for(int i = 1; i <= m; i ++) {
        scanf("%d%d%d",&x,&y,&w);
        a[x][y] = min(a[x][y],w);
    }
    dijkstra();
    if(dist[n] == INF) cout<<-1<<endl;
    else cout<<dist[n];
    return 0;
}
void dijkstra() {
    int x = 0;
    dist[1] = 0;
    for(int j = 1; j <= n; j ++) {
        x = 0;
        // 找到未标记点中dist最小的
        for(int i = 1; i <= n; i ++) {
            if(vis[i] == 0 && (x == 0 || dist[i] < dist[x])) {
                 x = i;
            }
        }
        vis[x] = 1;
        // 用全局最小值点更新其他节点(我们已经找到一个最小的距离,看那条边与这个最小距离有联系，然后更新)
        for(int i = 1; i <= n; i ++) {
            dist[i] = min(dist[i],dist[x] + a[x][i]);
        }
    }
    return ;
}