OJ-Problems-Source/HDOJ/5886_u012015746.cpp

#pragma comment(linker, "/STACK:102400000,102400000")
#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <cctype>
#include <map>
#include <set>
#include <queue>
#include <bitset>
#include <string>
#include <complex>
using namespace std;
typedef pair<int,int> Pii;
typedef long long LL;
typedef unsigned long long ULL;
typedef double DBL;
typedef long double LDBL;
#define MST(a,b) memset(a,b,sizeof(a))
#define CLR(a) MST(a,0)
#define SQR(a) ((a)*(a))
#define PCUT puts("\n----------")

const int maxn=1e5+10;;
struct Graph
{
    int ndn, edn, last[maxn];
    int u[2*maxn], v[2*maxn], w[2*maxn], nxt[2*maxn];
    void init(int _n){ndn=_n; edn=0; MST(last,-1);}
    void adde(int _u, int _v, int _w)
    {
        u[edn]=_u; v[edn]=_v; w[edn]=_w;
        nxt[edn]=last[_u];
        last[_u] = edn++;
    }
};

int N;
Graph G;
int dp[maxn][4], pos[maxn][4], dp2[maxn][3], pos2[maxn][3], res[maxn];
LL ans;

void add(int,int,int);
void add2(int,int,int);
int dfs0(int,int);
int dfs1(int,int,int,int);

int main()
{
    #ifdef LOCAL
    freopen("in.txt", "r", stdin);
//  freopen("out.txt", "w", stdout);
    #endif

    int T;
    scanf("%d", &T);
    for(int ck=1; ck<=T; ck++)
    {
        scanf("%d", &N);
        G.init(N);
        for(int i=1, u, v, w; i<N; i++)
        {
            scanf("%d%d%d", &u, &v, &w);
            G.adde(u,v,w); G.adde(v,u,w);
        }
        ans = 0;
        dfs0(1,0);
        dfs1(1,0,0,0);
        printf("%lld\n", ans);
    }
    return 0;
}

void add(int u, int v, int val)
{
    dp[u][3] = val; pos[u][3] = v;
    for(int i=2; i>=0; i--) if(dp[u][i] < dp[u][i+1])
    {
        swap(dp[u][i], dp[u][i+1]);
        swap(pos[u][i], pos[u][i+1]);
    }
}

void add2(int u, int v, int val)
{
    dp2[u][2] = val; pos2[u][2] = v;
    for(int i=1; i>=0; i--) if(dp2[u][i] < dp2[u][i+1])
    {
        swap(dp2[u][i], dp2[u][i+1]);
        swap(pos2[u][i], pos2[u][i+1]);
    }
}

int dfs0(int u, int f)
{
    MST(dp[u],-1); MST(pos[u],-1); 
    MST(dp2[u], -1); MST(pos2[u], -1);
    res[u] = 0;
    bool leaf=1;
    for(int e=G.last[u], v; ~e; e=G.nxt[e]) if((v=G.v[e])!=f)
    {
        leaf=0;
        add(u, v, dfs0(v,u)+G.w[e]);
        add2(u, v, res[v]);
        res[u] = max(res[u], res[v]);
    }
    if(leaf) add(u, u, 0);
    res[u] = max(res[u], max(dp[u][0], dp[u][0]+dp[u][1]));
    return dp[u][0];
}

int dfs1(int u, int f, int one, int two)
{
    for(int e=G.last[u], v; ~e; e=G.nxt[e]) if((v=G.v[e])!=f)
    {
        int tmax=0, tp=-1, tmax2=0, none, ntwo;
        for(int i=0; i<3 && ~dp[u][i]; i++)
        {
            if(pos[u][i] == v) continue;
            if(dp[u][i]>tmax) tmax = dp[u][i], tp=i;
        }
        none = max(tmax, one);
        ntwo = max(two, one+tmax);
        for(int i=0; i<3 && ~dp[u][i]; i++)
        {
            if(pos[u][i] == v || i==tp) continue;
            tmax2 = max(tmax2, dp[u][i]);
        }
        ntwo = max(ntwo, tmax + tmax2);
        if(pos[u][0] == v) ntwo = max(ntwo, dp2[u][1]);
        else ntwo = max(ntwo, dp2[u][0]);
        ans += max(ntwo, res[v]);
        dfs1(v, u, none+G.w[e], ntwo);
    }

}