Bellman_ford算法 可以求有限制边

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

using namespace std;

const int N=510,M=10010;

struct 
{
	int a,b,weight;
}e[M];

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

int Bellman_ford()
{
	memset(dist,0x3f,sizeof(dist));
	dist[1]=0;
	
	for(int i=0;i<k;i++)
	{
		memcpy(backup,dist,sizeof(dist));
		
		for(int j=0;j<m;j++)
		{
			int a=e[j].a,b=e[j].b,c=e[j].weight;
			
			dist[b]=min(dist[b],backup[a]+c);
		}
	}
	
	if(dist[n] > 0x3f3f3f3f/2)
	return  -1;
	return dist[n];
}

int main()
{
	cin>>n>>m>>k;
	for(int i=0;i<m;i++)
	{
		int a,b,c;
		cin>>a>>b>>c;
		e[i]={a,b,c};
	}
	
	int t=Bellman_ford();
	
	if(t==-1)
	puts("impossible");
	else
	printf("%d\n",t);
	
	return 0;
}