UVa1599 - Ideal Path

#include<cstdio>
#include<cstring>
#include<vector>
#include<queue>
using namespace std;
const int maxn=100010;
const int inf=1<<30;
int n,vis[maxn],d[maxn];
vector<int> g[maxn],ans;
struct way{
    int u,v,c;
    way(int u=0,int v=0,int c=0):u(u),v(v),c(c){}
};
vector<way> ways;
void build(int u,int v,int c){
    ways.push_back(way(u,v,c));
    int i=(int)ways.size()-1;
    g[u].push_back(i);

}
void rev_bfs(){
    memset(vis,0,sizeof(vis));
    d[n-1]=0;
    vis[n-1]=true;
    queue<int>q;
    q.push(n-1);
    while(!q.empty()){

        int v=q.front();
        q.pop();
        for(int i=0;i<g[v].size();i++)
        {
            int e=g[v][i];
            int u=ways[e].v;
            if(!vis[u]){

                vis[u]=true;
                d[u]=d[v]+1;
                q.push(u);

            }
        }
    }
}
void bfs()

{
    memset(vis,0,sizeof(vis));
    ans.clear();
    vis[0]=true;
    vector<int>next;
    next.push_back(0);
    for(int i=0;i<d[0];i++){
        int min_color=inf;
        for(int j=0;j<next.size();++j){
            int u=next[j];
            for(int k=0;k<g[u].size();++k)
        {
            int e=g[u][k];
            int v=ways[e].v;
            if(d[u]==d[v]+1)
                min_color=min(min_color,ways[e].c);
        }
    }
    ans.push_back(min_color);
    vector<int> next2;
    for(int j=0;j<next.size();j++){
        int u=next[j];
        for(int k=0;k<g[u].size();k++){
            int e=g[u][k];
            int v=ways[e].v;
            if(d[u]==d[v]+1&&!vis[v]&&ways[e].c==min_color){
                vis[v]=true;
                next2.push_back(v);
            }
        }
    }
    next=next2;


    }
    printf("%d\n",(int)ans.size());
    for(int i=0;i<ans.size();i++){

        if(i) printf(" ");
        printf("%d", ans[i]);
    }
    printf("\n");
}
int main()
{
    int u,v,c,m;
    while(~scanf("%d%d",&n,&m)){

        ways.size();
        for(int i=0;i<n;i++)
            g[i].clear();
        while(m--){
            scanf("%d%d%d",&u,&v,&c);
            build(u-1,v-1,c);
            build(v-1,u-1,c);
        }
        rev_bfs();
        bfs();
    }
    return 0;
}