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acwing 849

圣杰 2022-02-05 阅读 49
#include <bits/stdc++.h>

using namespace std;

const int N = 510;

int n, m;
int a[N][N];
int dist[N];
bool vist[N];

int main()
{
    cin >> n >> m;
    memset(a, 0x3f3f3f3f, sizeof a);
    for (int i = 1; i <= m; i ++)
    {
        int x, y, z;
        cin >> x >> y >> z;
        a[x][y] = min(a[x][y], z);
        //a[y][x] = z;
    }
    memset(dist, 0x3f, sizeof dist);
    memset(vist, false, sizeof vist);
    
    for (int i = 1; i <= n; i ++) a[i][i] = 0;
    dist[1] = 0;

    for (int cnt = 1; cnt <= n; cnt ++)
    {
        int max_n = 0x3f3f3f3f, x;
        for (int i = 1; i <= n; i ++) 
            if (!vist[i] && dist[i] < max_n)
                max_n = dist[i], x = i;
        vist[x] = true;
        for (int y = 1; y <= n; y ++) 
            dist[y] = min(dist[y], dist[x] + a[x][y]);
    }
    
    if (dist[n] >= 0x3f3f3f3f) cout << -1 << endl;
    else cout << dist[n] << endl;
    return 0;
}
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