Bellman_Ford算法

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

using namespace std;

const int N = 510, M = 10010;

struct Edge
{
    int a, b, w;
}edges[M];

int n, m, k;
int dist[N];
int last[N];

void bellman_ford()
{
    memset(dist, 0x3f, sizeof dist);

    dist[1] = 0;

    for (int i = 0; i < k; i ++ )
    {
        memcpy(last, dist, sizeof dist);
        for (int j = 0; j < m; j ++ )
        {
            auto e = edges[j];
            dist[e.b] = min(dist[e.b], last[e.a] + e.w);
        }
    }
}

int main()
{
    scanf("%d%d%d", &n, &m, &k);

    for (int i = 0; i < m; i ++ )
    {
        int a, b, w;
        cin >> a >> b >> w;
        edges[i] = {a, b, w};
    }

    bellman_ford();

    if (dist[n] > 0x3f3f3f3f / 2) puts("impossible");
    else printf("%d\n", dist[n]);

    return 0;
}