hdu5102 单位边权树上的前k长路径和：队列技巧
单向拓展边orz题解==
1 #include<stdio.h> 2 #include<string.h> 3 #include<algorithm> 4 #include<queue> 5 using namespace std; 6 int next[200005],head[200005],point[200005],now; 7 void add(int x,int y) 8 { 9 next[++now]=head[x]; 10 head[x]=now; 11 point[now]=y; 12 } 13 struct dian{ 14 int u,v,t; 15 }; 16 queue<dian>q; 17 int main() 18 { 19 int T,n,k,i,x,y,cnt,ans,tmp; 20 dian n1,n2; 21 scanf("%d",&T); 22 while (T--) 23 { 24 while (!q.empty()) q.pop(); 25 memset(head,-1,sizeof(head)); 26 scanf("%d%d",&n,&k); 27 now=0; k*=2; 28 for (i=1;i<n;i++) 29 { 30 scanf("%d%d",&x,&y); 31 add(x,y); add(y,x); 32 n1.u=x; n1.v=y; n1.t=1; q.push(n1); 33 n1.u=y; n1.v=x; n1.t=1; q.push(n1); 34 } 35 cnt=0; ans=0; 36 if (k==0) {printf("0\n"); continue;} 37 while (!q.empty()) 38 { 39 n1=q.front(); q.pop(); 40 cnt++; ans+=n1.t; 41 if (cnt==k) break; 42 tmp=cnt+q.size(); 43 for (i=head[n1.v];i!=-1&&tmp<=k;i=next[i]) 44 { 45 x=point[i]; 46 if (x==n1.u) continue; 47 n2.u=n1.v; n2.v=x; n2.t=n1.t+1; 48 q.push(n2); tmp++; 49 } 50 } 51 printf("%d\n",ans/2); 52 } 53 }
