AcWing 853. 有边数限制的最短路

Bellman-Ford

基于迭代思想的暴力，而非贪心

// 853.有边数限制的最短路
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 510;
const int M = 10010;
const int INF = 0x3f3f3f3f;
int head[N],e[M],w[M],net[M],cnt;
int n,m,k;
int dis[N],temp[N];
void init() {
    cnt=0;
    fill(head,head+N,0);
    return;
}
void addedge(int x, int y, int z) {
    ++cnt;
    e[cnt]=y;
    w[cnt]=z;
    net[cnt]=head[x];
    head[x]=cnt;
    return;
}
void bellmanford() {
    fill(dis,dis+N,INF);
    dis[1]=0;
    for(int i=1;i<=k;++i) {
        for(int x=1;x<=n;++x) temp[x]=dis[x];
        for(int x=1;x<=n;++x) {
            for(int p=head[x];p;p=net[p]) {
                int y=e[p];
                int z=w[p];
                if(temp[x]!=INF&&dis[y]>temp[x]+z) {
                    dis[y]=temp[x]+z;
                }
            }
        }
    }
    return;
}
int main() {
    #ifdef ONLINE_JUDGE
    #else
    freopen("in.txt","r",stdin);
    freopen("out.txt","w",stdout);
    #endif
    init();
    scanf("%d%d%d",&n,&m,&k);
    for(int i=0;i<m;++i) {
        int x,y,z;
        scanf("%d%d%d",&x,&y,&z);
        addedge(x,y,z);
    }
    bellmanford();
    if(dis[n]==INF) printf("impossible");
    else printf("%d",dis[n]);
    return 0;
}