创一个复制数组，再不断更新路径，防止一直更新到尾

#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;

#define INF 5000000
#define N 10000

int dis[N],f[N],k,n,m;

struct edge
{
    int a,b,w;
}e[N];

int main()
{
    cin >>n >>m >>k;
    for (int i = 1; i <= m; i++)
    {
        int a,b,w;
        cin >>a >> b>> w;
        e[i] = {a,b,w};
    }
    memset(dis,0x3f,sizeof dis);
    dis[1] = 0;
    for (int i = 1; i <= k; i++)
    {
        memcpy(f , dis, sizeof dis);
        for (int j = 1; j <= m; j++)
        {
            int a = e[j].a,b = e[j].b,w = e[j].w;
            if (f[a] != 0x3f3f3f3f && dis[b] > f[a] + w)
                dis[b] = f[a] + w;
        } 
    }
    if (dis[n] == 0x3f3f3f3f)
    {
        puts("impossible");
        return 0;
    }
    cout <<dis[n]; 
}