AIM Tech Round 3 (Div. 2) E. centroids

Exercises

Tree-shaped DP

A very good topic.

Test instructions

For each point. Change an edge to make this point the center of the tree

Exercises

The so-called center of Gravity: refers to the maximum number of connected components after removing this point <=N/2

For each point, divided into downward analysis, upward analysis

Down analysis: Find the maximum node of the child node of the point U v. Then find the maximum child node of node V that is less than or equal to N/2, connected to U

Analyze up: Find the maximum node of the parent node of the point U v. If V==u so. Find the second largest node W. Then find the maximum child node of the child node of the point less than or equal to N/2, connected to U

Down analysis and up analysis only need to judge one, because the points greater than N/2 only one

Code reference: Http://blog.csdn.net/u014258433/article/details/52454105?locationNum=9

Code:

#include <bits/stdc++.h>#defineMAXN 400010#defineMoD 1000000007#definell Long Long#definePB Push_back#defineFS First#defineSe Secondusing namespacestd;Const intinf=1e9+7;intN;vector<int>G[MAXN];intFSON[MAXN],SSON[MAXN],UP[MAXN],DW[MAXN];intSIZ[MAXN],ANS[MAXN];voidDfsintUintFA) {Siz[u]=1; Fson[u]=sson[u]=0;  for(intI=0; I<g[u].size (); i++)    {        intv=G[u][i]; if(V==FA)Continue;        DFS (V,U); Siz[u]+=Siz[v]; if(Dw[v]>sson[u]) sson[u]=Dw[v]; if(fson[u]<Sson[u]) swap (fson[u],sson[u]); } Dw[u]=Fson[u]; if(siz[u]<=n/2) dw[u]=siz[u];}voidDFS1 (intUintFA) {    if(fa!=-1) {Up[u]=Max (UP[U],UP[FA]); if(Dw[u]!=fson[fa]) up[u]=Max (UP[U],FSON[FA]); Elseup[u]=Max (UP[U],SSON[FA]); if(n-siz[u]<=n/2) up[u]=n-Siz[u]; }    inttmp=0;  for(intI=0; I<g[u].size (); i++)    {        intv=G[u][i]; if(V==FA)Continue;        DFS1 (V,u); if(siz[v]>n/2) tmp=v; }    if(n-siz[u]>n/2) tmp=-1; if(!tmp) ans[u]=1; Else if(tmp>0)    {        if(siz[tmp]-dw[tmp]<=n/2) ans[u]=1; }     Else if(n-siz[u]-up[u]<=n/2) ans[u]=1;}intMain () {CIN>>N;  for(intI=1; i<n;i++)    {        intx, y; CIN>>x>>y;        G[X].PB (y);    G[Y].PB (x); } DFS (1,-1); DFS1 (1,-1);  for(intI=1; i<=n;i++) printf ("%d", Ans[i]); printf ("\ n"); return 0;}

AIM Tech Round 3 (Div. 2) E. centroids