BZOJ 1579 道路升级 Dijkstra

思路：

这道题 不能把所有边都建出来 会MLE的！！！

oh gosh

其实不建所有的边 用的时候再调就行了….（也没啥区别）

//By SiriusRen
#include <queue>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
#define N 100050
int n,m,k,first[N],v[N],w[N],next[N],tot,dis[N][21],vis[N][21],xx,yy,zz;
void add(int x,int y,int z){
    w[tot]=z,v[tot]=y,next[tot]=first[x],first[x]=tot++;
}
struct Node{int now,level,weight;}jy;
bool operator < (Node a,Node b){return a.weight>b.weight;}
void Dijkstra(){
    memset(dis,0x3f,sizeof(dis)),dis[1][0]=0;
    priority_queue<Node>pq;
    jy.now=1,pq.push(jy);
    while(!pq.empty()){
        Node t=pq.top();pq.pop();
        if(vis[t.now][t.level])continue;
        vis[t.now][t.level]=1;
        for(int i=first[t.now];~i;i=next[i]){
            if(!vis[v[i]][t.level]&&dis[v[i]][t.level]>dis[t.now][t.level]+w[i]){
                dis[v[i]][t.level]=dis[t.now][t.level]+w[i];
                jy.level=t.level,jy.now=v[i],jy.weight=dis[v[i]][t.level],pq.push(jy);
            }
            if(t.level<k&&!vis[v[i]][t.level+1]&&dis[v[i]][t.level+1]>dis[t.now][t.level]){
                dis[v[i]][t.level+1]=dis[t.now][t.level];
                jy.level=t.level+1,jy.now=v[i],jy.weight=dis[t.now][t.level],pq.push(jy);
            }
        }
    }
}
int main(){
    memset(first,-1,sizeof(first));
    scanf("%d%d%d",&n,&m,&k);
    for(int i=1;i<=m;i++){
        scanf("%d%d%d",&xx,&yy,&zz);
        add(xx,yy,zz),add(yy,xx,zz);
    }
    Dijkstra();
    printf("%d\n",dis[n][k]);
}