hdu 4123 树形DP+单调队列

http://acm.hust.edu.cn/vjudge/problem/25790

这题基本同poj 3162

要注意mx,mx2,vx,vx2每次都要初始化

#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <cctype>
#include <vector>
#include <iterator>
#include <set>
#include <map>
#include <sstream>
using namespace std;

#define mem(a,b) memset(a,b,sizeof(a))
#define pf printf
#define sf scanf
#define spf sprintf
#define pb push_back
#define debug printf("!
")
#define MAXN 50000+5
#define MAX(a,b) a>b?a:b
#define blank pf("
")
#define LL long long
#define ALL(x) x.begin(),x.end()
#define INS(x) inserter(x,x.begin())
#define pqueue priority_queue
#define INF 0x3f3f3f3f

#define ls (rt<<1)
#define rs (rt<<1|1)

int n,m;

int head[MAXN],vis[MAXN],ptr=1;

int mx[MAXN],mx2[MAXN],vx[MAXN],vx2[MAXN];

int p1[MAXN],p2[MAXN],ans;

struct node{int y,next,val;}tree[MAXN<<2];

void init()
{
    mem(head,-1);
    mem(vis,0);
    mem(mx,0);
    mem(mx2,0);
    mem(vx,0);
    mem(vx2,0);
    ptr = 1;
}

void add(int son,int fa,int val)
{
    tree[ptr].y=son;
    tree[ptr].val=val;
    tree[ptr].next=head[fa];
    head[fa]=ptr++;
}

void dfs(int root,int fa)
{
    for(int i = head[root];i!=-1;i=tree[i].next)
    {
        int y = tree[i].y;
        if(y==fa) continue;
        dfs(y,root);
        if(mx2[root]<mx[y]+tree[i].val)
        {
            vx2[root] = y;
            mx2[root] = mx[y]+tree[i].val;
            if(mx2[root]>mx[root])
            {
                swap(vx2[root],vx[root]);
                swap(mx2[root],mx[root]);
            }
        }
    }
}

void dfs2(int root,int fa)
{
    for(int i = head[root];i!=-1;i=tree[i].next)
    {
        int y = tree[i].y;
        if(y==fa) continue;
        if(y == vx[root])
        {
            if(mx2[root]+tree[i].val > mx2[y])
            {
                mx2[y] = mx2[root]+tree[i].val;
                vx2[y] = root;
                if(mx2[y]>mx[y])
                {
                    swap(vx2[y],vx[y]);
                    swap(mx2[y],mx[y]);
                }
            }
        }
        else
        {
            if(mx[root]+tree[i].val > mx2[y])
            {
                mx2[y] = mx[root]+tree[i].val;
                vx2[y] = root;
                if(mx2[y]>mx[y])
                {
                    swap(vx2[y],vx[y]);
                    swap(mx2[y],mx[y]);
                }
            }
        }
        dfs2(y,root);
    }
}

void getL(int q)
{
    int h1,h2,r1,r2,pre;
    h1=h2=pre=1;
    r1=r2=ans=0;
    for(int i=1;i<=n;i++)
    {
        while(h1<=r1 && mx[p1[r1]]>=mx[i]) r1--;
        p1[++r1] = i;
        while(h2<=r2 && mx[p2[r2]]<=mx[i]) r2--;
        p2[++r2] = i;
        while(h1<=r1 && h2<=r2 && mx[p2[h2]]-mx[p1[h1]]>q)
        {
            if(p1[h1]>p2[h2]) pre = p2[h2++]+1;
            else pre = p1[h1++]+1;
        }
        if(h1<=r1 && h2<=r2 && mx[p2[h2]]>=mx[p1[h1]])
        {
            ans = max(ans,i-pre+1);
        }
    }
}



int main()
{
    int i,j;
    while(~sf("%d%d",&n,&m),m+n)
    {
        init();
        for(i=2;i<=n;i++)
        {
            int x,y,z;
            sf("%d%d%d",&x,&y,&z);
            add(y,x,z);
            add(x,y,z);
        }
        dfs(1,0);
        dfs2(1,0);
        /*
        for(i=1;i<=n;i++) pf("%d ",mx[i]);
        blank;
        */
        int q;
        for(i=0;i<m;i++)
        {
            mem(p1,0);
            mem(p2,0);
            sf("%d",&q);
            getL(q);
            pf("%d
",ans);
        }
    }
}