SGU149 Computer Network

#include<iostream>
#include<cstdio>
#include<vector>
#include<cstring>
#include<cmath>
#include<queue>
using namespace std;
#define pb push_back
#define mp make_pair
#define se second
#define fs first
#define ll long long
#define CLR(x) memset(x,0,sizeof x)
#define MC(x,y) memcpy(x,y,sizeof(x))  
#define SZ(x) ((int)(x).size())
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1 
#define INF 2097152
typedef pair<int,int> P;
const double eps=1e-9;
const int maxn=10100;
const int mod=1e9+7;

int First_son[maxn],Second_son[maxn],First_fa[maxn];
int First_son_point[maxn];

struct Edge{
    int to,nxt,w;
}edge[maxn*2];

int head[maxn],p[maxn];
int cnt,n,u,w;

void addEdge(int u,int v,int w){
    edge[cnt].to=v;
    edge[cnt].w=w;
    edge[cnt].nxt=head[u];
    head[u]=cnt++;
}

//将无根树化为有根树，根为1 
void dfs(int u,int fa){
    p[u]=fa;
    for(int i=head[u];i!=-1;i=edge[i].nxt){
        int v=edge[i].to;
        if(v!=fa) dfs(v,u);
    }
}


//找子树中的最远节点和次远节点，因为是子树，是从下到上更新，先dfs1 
void dfs1(int u){
    First_son[u]=Second_son[u]=0;
    for(int i=head[u];i!=-1;i=edge[i].nxt){
        int v=edge[i].to;
        if(v==p[u]) continue;
        dfs1(v);
        if(Second_son[u]<First_son[v]+edge[i].w){
            Second_son[u]=First_son[v]+edge[i].w;
            if(First_son[u]<Second_son[u]){
                First_son_point[u]=v;
                swap(First_son[u],Second_son[u]);
            }
        }
    }
}


//找寻父节点中的最远节点，是从上到下，所以是后dfs2 
void dfs2(int u){
    for(int i=head[u];i!=-1;i=edge[i].nxt){
        int v=edge[i].to;
        if(v==p[u]) continue;
        if(v==First_son_point[u]) First_fa[v]=edge[i].w+max(Second_son[u],First_fa[u]);
        else                      First_fa[v]=edge[i].w+max(First_son[u],First_fa[u]);
        dfs2(v);
    }
}


int main(){
    cnt=0;
    memset(head,-1,sizeof(head));
    scanf("%d",&n);
    for(int v=2;v<=n;v++){
        scanf("%d%d",&u,&w);
        addEdge(u,v,w);
        addEdge(v,u,w);
    }
    dfs(1,-1);
    dfs1(1);
    dfs2(1);
    for(int i=1;i<=n;i++) printf("%d\n",max(First_son[i],First_fa[i]));
    return 0;
}