HDU2196 computer (tree-shaped DP)

Like LightOJ1257, I used a tree to divide and write. In fact, this problem is a classic tree-shaped DP, feel this DP is not simple.

• Dp[0][u] represents the maximum distance from a node in a subtree with u as the root
• Dp[1][u] Represents the sub-distance between the nodes and U in a subtree with u as root

These two can be transferred once more by DFS through the son node. Obviously Dp[0][u] is a possible answer to u, that is, the furthest distance you go down , and the missing part is the furthest distance you go up :

• Dp[2][u] Indicates the farthest distance you go up

For this transfer, in two cases, this is the case:

1. DP[2][V] = max (Dp[0][u]+weight (u,v), Dp[2][u]+weight (u,v)) (V is the son of U and U goes down the farthest distance without going through V)
2. DP[2][V] = max (Dp[1][u]+weight (u,v), Dp[2][u]+weight (u,v)) (V is the son of U and U goes down the farthest distance through V)

DFS can get it again.

1#include <cstdio>2#include <cstring>3#include <algorithm>4 using namespacestd;5 #defineMAXN 111116 structedge{7     intV,w,next;8}edge[maxn<<1];9 intNE,HEAD[MAXN];Ten voidAddedge (intUintVintW) { OneEdge[ne].v=v; edge[ne].w=W; AEdge[ne].next=head[u]; head[u]=ne++; - } - Long Longd[3][MAXN]; the intIDX[MAXN]; - voidDfs0 (intUintFA) { -     Long Longmx0=0, mx1=0; -      for(intI=head[u]; i!=-1; I=Edge[i].next) { +         intv=edge[i].v; -         if(V==FA)Continue; + Dfs0 (v,u); A         if(mx0<=d[0][V]+EDGE[I].W) mx1=mx0,mx0=d[0][v]+edge[i].w,idx[u]=v; at         Else if(mx1<d[0][V]+EDGE[I].W) mx1=d[0][v]+EDGE[I].W; -         Else if(mx1<d[1][V]+EDGE[I].W) mx1=d[1][v]+EDGE[I].W; -     } -d[0][u]=mx0; d[1][u]=MX1; - } - voidDFS1 (intUintFA) { in      for(intI=head[u]; i!=-1; I=Edge[i].next) { -         intv=edge[i].v; to         if(V==FA)Continue; +         if(IDX[U]==V) d[2][v]=max (d[1][u]+edge[i].w,d[2][u]+EDGE[I].W); -         Elsed[2][v]=max (d[0][u]+edge[i].w,d[2][u]+EDGE[I].W); the DFS1 (v,u); *     } $ }Panax Notoginseng intMain () { -     intn,a,b; the      while(~SCANF ("%d",&N)) { +Ne=0; Amemset (head,-1,sizeof(head)); the          for(intI=2; i<=n; ++i) { +scanf"%d%d",&a,&b); - Addedge (i,a,b); Addedge (a,i,b); $         } $memset (D,0,sizeof(d)); -Dfs0 (1,1); -DFS1 (1,1); the          for(intI=1; i<=n; ++i) { -printf"%lld\n", Max (d[0][i],d[2][i]));Wuyi         } the     } -     return 0; Wu}

HDU2196 computer (tree-shaped DP)