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 100050int 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]);}