C++ 代码

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdio>
using namespace std;
const int N = 510, M = 1e4+10;

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

struct node{
    int a, b, c;
}edge[M];

void bellman_ford()
{
    //初始化不能忘！
    memset(dist, 0x3f, sizeof(dist));
    dist[1] = 0;

    //一共更新K次
    for(int i = 0; i < k; i++)
    {
        //备份一下
        memcpy(last, dist, sizeof(dist));

        for(int j = 0; j < m; j++)
        {
            node e = edge[j];
            dist[e.b] = min(dist[e.b] , last[e.a] + e.c);
        }
    }
}


int main()
{
    scanf("%d%d%d", &n, &m, &k);
    for(int i = 0; i < m; i++)
    {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        edge[i] = {a, b, c};
    }

    bellman_ford();

    //存在负权边，所以n点不一定是正无穷
    if(dist[n] > 0x3f3f3f3f / 2) puts("impossible");

    else printf("%d\n", dist[n]);

    return 0;
}