HDU 2196 Computer（樹形DP求最長路）

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Problem DescriptionA school bought the first computer some time ago(so this computer‘s id is 1). During the recent years the school bought N-1 new computers. Each new computer was connected to one of settled earlier. Managers of school are anxious about slow functioning of the net and want to know the maximum distance Si for which i-th computer needs to send signal (i.e. length of cable to the most distant computer). You need to provide this information. 


Hint: the example input is corresponding to this graph. And from the graph, you can see that the computer 4 is farthest one from 1, so S1 = 3. Computer 4 and 5 are the farthest ones from 2, so S2 = 2. Computer 5 is the farthest one from 3, so S3 = 3. we also get S4 = 4, S5 = 4. 
InputInput file contains multiple test cases.In each case there is natural number N (N<=10000) in the first line, followed by (N-1) lines with descriptions of computers. i-th line contains two natural numbers - number of computer, to which i-th computer is connected and length of cable used for connection. Total length of cable does not exceed 10^9. Numbers in lines of input are separated by a space. 
OutputFor each case output N lines. i-th line must contain number Si for i-th computer (1<=i<=N). 
Sample Input

51 12 13 11 1

 
Sample Output

32344

 

在一個樹種求每個點的最長路：

dp[x]表示經過邊x的最長路..

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>typedef long long LL;using namespace std;#define REPF( i , a , b ) for ( int i = a ; i <= b ; ++ i )#define REP( i , n ) for ( int i = 0 ; i < n ; ++ i )#define CLEAR( a , x ) memset ( a , x , sizeof a )const int maxn=10010;struct node{    int u,v;    int w;    int next;}e[maxn<<1];int head[maxn];int dp[maxn<<1];int n,cnt;void add(int u,int v,int w){    e[cnt].u=u;e[cnt].v=v;    e[cnt].w=w;e[cnt].next=head[u];    head[u]=cnt++;}int dfs(int u,int p){    int ans=0;    for(int i=head[u];~i;i=e[i].next)    {        int v=e[i].v;        if(v==p)   continue;        if(dp[i]==0)   dp[i]=dfs(v,u)+e[i].w;        ans=max(ans,dp[i]);    }    return ans;}int main(){    int x,y;    while(~scanf("%d",&n))    {        CLEAR(head,-1);        CLEAR(dp,0);        cnt=0;        REPF(i,2,n)        {            scanf("%d%d",&x,&y);            add(i,x,y);            add(x,i,y);        }        for(int i=1;i<=n;i++)            printf("%d\n",dfs(i,i));    }    return 0;}

HDU 2196 Computer（樹形DP求最長路）