HDU 2196 Computer

Main topic

Give you a tree with a weighted edge, and find the distance from each point of the tree to its farthest point.

Analysis

Classic Tree DP problem. Because for a node, the path that might get the maximum distance from his subtree, or from his parent node, is used two times by DFS.

However, one problem is to judge the maximum value of a point from the parent node, then if the maximum value of his parent node is exactly from that point, then it loses the state from the parent node, so record the maximum of two values.

1#include <cstdio>2#include <cstring>3#include <cmath>4#include <string>5#include <iostream>6#include <algorithm>7#include <Set>8 #defineMAXN 200109 using namespacestd;Ten structNode One { A     intv,w; -     intNext; - }NODE[MAXN]; the intTot,n; - intHEAD[MAXN],MAXN[MAXN],SMAXN[MAXN],MAXID[MAXN],SMAXID[MAXN]; - voidAddintUintVintW) - { +node[tot].v=v; -node[tot].w=W; +node[tot].next=Head[u]; Ahead[u]=tot; attot++; - } - voidDFS1 (intUintp) - { -maxn[u]=0; -smaxn[u]=0; in      for(inti=head[u];i!=-1; i=node[i].next) -     { to         intv=node[i].v; +         if(v==p) -             Continue; the DFS1 (v,u); *         if(smaxn[u]<maxn[v]+NODE[I].W) $         {Panax Notoginsengsmaxn[u]=maxn[v]+NODE[I].W; -smaxid[u]=v; the             if(smaxn[u]>Maxn[u]) +             { A swap (smaxn[u],maxn[u]); the swap (smaxid[u],maxid[u]); +             } -         } $     } $ } - voidDFS2 (intUintp) - { the      for(inti=head[u];i!=-1; i=node[i].next) -     {Wuyi         intv=node[i].v; the         if(v==p) -             Continue; Wu         if(v==Maxid[u]) -         { About             if(node[i].w+smaxn[u]>Smaxn[v]) $             { -  -smaxn[v]=node[i].w+Smaxn[u]; -smaxid[v]=u; A                 if(smaxn[v]>Maxn[v]) +                 { the swap (smaxn[v],maxn[v]); - swap (smaxid[v],maxid[v]); $                 } the             } the         } the         Else the         { -             if(node[i].w+maxn[u]>Smaxn[v]) in             { thesmaxn[v]=node[i].w+Maxn[u]; thesmaxid[v]=u; About                 if(smaxn[v]>Maxn[v]) the                 { the swap (smaxn[v],maxn[v]); the swap (maxid[v],smaxid[v]); +                 } -             } the         }Bayi DFS2 (v,u); the  the     } - } - intMain () the { the      while(SCANF ("%d", &n)! =EOF) the     { thetot=0; -         intv,w; thememset (head,-1,sizeof(head)); the          for(intI=2; i<=n;i++) the         {94scanf"%d%d",&v,&W); the Add (i,v,w); the Add (v,i,w); the         }98DFS1 (1,-1); AboutDFS2 (1,-1); -          for(intI=1; i<=n;i++)101printf"%d\n", Maxn[i]);102 103     }104     return 0; the}

Diagram is saved with adjacency table, do not understand can see my previous blog

HDU 2196 Computer