原题链接 https://www.acwing.com/problem/content/851/
//注意一下下面注释当中对于j = 0的一个解释
#include<iostream>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
const int N = 510;
int n, m;
int g[N][N];
int dist[N];
bool st[N];
int dijkstra()
{
memset(dist, 0x3f, sizeof dist);
dist[1] = 0;
for(int i = 0; i < n - 1; i ++)
{
int t = -1;
for(int j = 1; j <= n; j ++)//j = 0的时候t 每次都要经过j = 0的这个点,多迭代了一步但是对结果没有影响,也是没有意义的一步,本身节点中就没有0号节点
if(!st[j] && (t == -1 || dist[t] > dist[j]))
t = j;
for(int j = 1; j <= n; j ++)
dist[j] = min(dist[j], dist[t] + g[t][j]);
st[t] = true;
}
if(dist[n] == 0x3f3f3f3f) return -1;
return dist[n];
}
int main()
{
scanf("%d%d", &n, &m);
memset(g, 0x3f, sizeof g);
while(m --)
{
int a, b, c;
scanf("%d%d%d", &a, &b, &c);
g[a][b] = min(g[a][b], c);
}
printf("%d", dijkstra());
return 0;
}