HDU 2196 Computer 树形DP

求每个节点到距离他最远节点的距离。

//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<sstream>
#include<cmath>
#include<climits>
#include<string>
#include<map>
#include<queue>
#include<vector>
#include<stack>
#include<set>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
#define pb(a) push_back(a)
#define INF 0x1f1f1f1f
#define lson idx<<1,l,mid
#define rson idx<<1|1,mid+1,r
#define PI  3.1415926535898
template<class T> T min(const T& a,const T& b,const T& c) {
    return min(min(a,b),min(a,c));
}
template<class T> T max(const T& a,const T& b,const T& c) {
    return max(max(a,b),max(a,c));
}
void debug() {
#ifdef ONLINE_JUDGE
#else

    freopen("d:\in.txt","r",stdin);
   // freopen("d:\out1.txt","w",stdout);
#endif
}
int getch() {
    int ch;
    while((ch=getchar())!=EOF) {
        if(ch!=' '&&ch!='
')return ch;
    }
    return EOF;
}

const int maxn=10100;

struct EDGE
{
    int u,v,w;
    EDGE(){}
    EDGE(int a,int b,int c):u(a),v(b),w(c){}
};
vector<EDGE> e;
vector<int> g[maxn];

ll f1[maxn],f2[maxn];
int son1[maxn],son2[maxn];


ll StepOne(int x,int fa)
{
    f1[x]=0;f2[x]=0;
    son1[x]=-1;son2[x]=-1;
    for(int i=0;i<g[x].size();i++)
    {
        int v=e[g[x][i]].v,w=e[g[x][i]].w;
        if(v!=fa)
        {
            ll res=StepOne(v,x);

            if(res+w>=f1[x])
            {
                f2[x]=f1[x];
                son2[x]=son1[x];

                f1[x]=res+w;
                son1[x]=v;
            }
            else if(res+w>=f2[x])
            {
                f2[x]=res+w;
                son2[x]=v;
            }
        }
    }
    return f1[x];
}

int StepTwo(int x,int fa,int ei)
{
    if(fa!=-1)
    {
        if(son1[fa]!=x)
        {
            if(f1[fa]+e[ei].w>=f1[x])
            {
                f2[x]=f1[x];
                son2[x]=son1[x];

                f1[x]=f1[fa]+e[ei].w;
                son1[x]=fa;
            }else if(f1[fa]+e[ei].w>=f2[x])
            {
                f2[x]=f1[fa]+e[ei].w;
                son2[x]=fa;
            }
        }else
        {
            if(f2[fa]+e[ei].w>=f1[x])
            {
                f2[x]=f1[x];
                son2[x]=son1[x];

                f1[x]=f2[fa]+e[ei].w;
                son1[x]=fa;
            }else if(f2[fa]+e[ei].w>=f2[x])
            {
                f2[x]=f2[fa]+e[ei].w;
                son2[x]=fa;
            }
        }
    }

    for(int i=0;i<g[x].size();i++)
    {
        int v=e[g[x][i]].v;
        if(v!=fa)
        {
            StepTwo(v,x,g[x][i]);
        }
    }
    return 0;
}
void read(int n)
{
    for(int i=1;i<=n;i++)
        g[i].clear();
    e.clear();
    for(int i=2;i<=n;i++)
    {
        int v,w;
        scanf("%d%d",&v,&w);
        e.push_back(EDGE(i,v,w));
        g[i].push_back(e.size()-1);

        e.push_back(EDGE(v,i,w));
        g[v].push_back(e.size()-1);
    }
}
int main()
{
   // freopen("in.txt","r",stdin);
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        read(n);
        StepOne(1,-1);
        StepTwo(1,-1,-1);
        for(int i=1;i<=n;i++)
            printf("%I64d
",f1[i]);
    }
    return 0;
}