[Winter DAY1T3] Tree

Title Description Description

For a tree of n nodes without root, the number of simple paths of path length =k

Enter a description input Description

First row two positive integers n,k Next N-1 line, two positive integers per line x, Y, representing an edge (x, y)

Outputs description output Description

One line an integer, the answer

Sample input to sample

4 21 22) 32 4

Sample output Sample Outputs

3

Data Size & Hint

For 30% 2<=k,n<=1000 For 100%,2<=k,n<=10^5

Or a point division of the problem, and POJ1741 the only difference is that one is to find the path <=k, one is to find equals K. The only difference between the two algorithms is the difference between dealing with the dis array. For the number of O (n) in an ordered table to satisfy the sum of two numbers and equal to K, I can not think of any better method, so the processing of the ANS when the writing of the more ugly.

#include <iostream>#include<cmath>#include<algorithm>#include<cstring>#include<cstdio>#include<queue>using namespaceStd;typedefLong LongLL;#definePi ACOs (-1.0)inlineintRead () {intx=0, f=1;CharC=GetChar ();  while(!isdigit (c)) {if(c=='-') f=-1; c=GetChar ();}  while(IsDigit (c)) {x=x*Ten+c-'0'; c=GetChar ();} returnx*F;}Const intmaxn=100010;structedge{intU,v,next; Edge () {} Edge (int_1,int_2,int_3): U (_1), V (_2), Next (_3) {}}e[2*MAXN];intFirst[maxn],n,k,a,b,size[maxn],masize[maxn],now_size,root,dis[maxn],end;BOOLVIS[MAXN]; LL ans;voidAddedge (intIintAintb) {E[i]=Edge (A,b,first[a]); First[a]=i;}voidGetsintUintPA) {Size[u]=1; Masize[u]=0;  for(inti=first[u];i!=-1; i=e[i].next)if(!VIS[E[I].V] && e[i].v!=PA)            {gets (e[i].v,u); Size[u]+=SIZE[E[I].V]; Masize[u]=Max (Size[e[i].v],masize[u]); }}voidGETR (intRintUintPA) {Masize[u]=max (masize[u],size[r]-Size[u]); if(masize[u]<now_size) now_size=masize[u],root=u;  for(inti=first[u];i!=-1; i=e[i].next)if(!VIS[E[I].V] && e[i].v!=pa) getr (r,e[i].v,u);}voidGETD (intUintPaintd) {Dis[end++]=D;  for(inti=first[u];i!=-1; i=e[i].next)if(!VIS[E[I].V] && e[i].v!=pa) getd (e[i].v,u,d+1);} LL Calc (intUintd) {End=0; GETD (U,-1, D); LL ret=0; intL=0, r=end-1, L,r; Sort (Dis,dis+end); //cout<<u<< ":";//for (int i=0;i<end;i++) cout<<dis[i]<< ";//cout<<endl;     while(l<r) { while(dis[l]+dis[r]>k && l<r) r--; if(dis[l]+dis[r]==k) {if(dis[l]==Dis[r]) {ret+ = ((LL) (r-l+1) * (LL) (r-l)/2);  Break; }            Else{L=r=1;  while(dis[r-1]==dis[r]) R--, r++;  while(dis[l+1]==DIS[L]) l++,l++; RET+ = (ll) l* (LL) R); L=r=0; R--;l++; }        }        Elsel++; }    returnret;}voidDfsintu) {Now_size=N; Gets (U,-1); Getr (U,u,-1); Ans+=calc (Root,0); Vis[root]=1;  for(inti=first[root];i!=-1; i=e[i].next)if(!VIS[E[I].V]) {ans-=calc (E[I].V,1);        DFS (E[I].V); }    return;}intMain () {Freopen ("tree.in","R", stdin); Freopen ("Tree.out","W", stdout); memset (First,-1,sizeof(first)); N=read (); k=read ();  for(intI=0; i<n-1; i++) {a=read (); b=read (); Addedge (i*2, A, b); Addedge (i*2+1, B,a); } DFS (1); printf ("%lld\n", ans); return 0;}

[Winter DAY1T3] Tree