思路

code

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>

using namespace std;

const int N = 510;

bool st[N];
int dist[N];
int g[N][N];
int n, m;

int dijstra()
{
    memset(dist, 0x3f, sizeof dist);

    dist[1] = 0;

    for (int i = 0; i < n; i ++ )
    {
        int t = -1;  // t用来求所有st[] == false的节点中，dist[]最小的节点编号。

        for (int j = 1; j <= n; j ++ )
        {
            if (!st[j] && (t == -1 || dist[j] < dist[t]))
                t = j;
        }
        st[t] = true;    

        // 更新
        for (int j = 1; j <= n; j ++ )
            dist[j] = min(dist[j], dist[t] + g[t][j]);

    }

    if (dist[n] == 0x3f3f3f3f) return -1;
    else 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);
    }

    int t = dijstra();

    printf("%d\n", t);

    return 0;
}