BZOJ 3251 树上三角形

NOIP的东西回成都再说吧。。。

这题暴力。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxv 100500
#define maxe 200500
using namespace std;
int n,q,x,y,z,val[maxv],anc[maxv][],dis[maxv],g[maxv],nume=;
int s[maxv],top=;
struct edge
{
    int v,nxt;
}e[maxe];
void addedge(int u,int v)
{
    e[++nume].v=v;
    e[nume].nxt=g[u];
    g[u]=nume;
}
int read()
{
    char ch;int data=;
    while (ch<'' || ch>'') ch=getchar();
    while (ch>='' && ch<='')
    {
        data=data*+ch-'';
        ch=getchar();
    }
    return data;
}
void dfs(int x,int fath)
{
    for (int i=g[x];i;i=e[i].nxt)
    {
        int v=e[i].v;
        if (v!=fath)
        {
            anc[v][]=x;dis[v]=dis[x]+;
            dfs(v,x);
        }
    }
}
void get_table()
{
    for (int e=;e<=;e++)
        for (int i=;i<=n;i++)
            anc[i][e]=anc[anc[i][e-]][e-];
}
int lca(int x,int y)
{
    if (dis[x]<dis[y]) swap(x,y);
    for (int e=;e>=;e--)
    {
        if ((dis[anc[x][e]]>=dis[y]) && (anc[x][e]))
           x=anc[x][e];
    }
    if (x==y) return x;
    for (int e=;e>=;e--)
    {
        if (anc[x][e]!=anc[y][e])
        {
            x=anc[x][e];
            y=anc[y][e];
        }
    }
    return anc[x][];
}
void get_push(int t)
{
    top=;
    while (x!=t) {s[++top]=val[x];x=anc[x][];}
    while (y!=t) {s[++top]=val[y];y=anc[y][];}
    s[++top]=val[t];
}
void ask()
{
    int t=lca(x,y),tot=dis[x]+dis[y]-dis[t]-dis[anc[t][]];
    if (tot>) {printf("Y\n");return;}
    get_push(t);
    sort(s+,s+top+);
    int flag=;
    for (int i=;i<=top-;i++)
    {
        if ((long long)s[i]+(long long)s[i+]>(long long)s[i+])
           flag=;
    }
    if (flag) printf("N\n");
    else printf("Y\n");
}
int main()
{
    n=read();q=read();
    for (int i=;i<=n;i++) val[i]=read();
    for (int i=;i<=n-;i++)
    {
          x=read();y=read();
          addedge(x,y);addedge(y,x);
    }
    dis[]=;dfs(,);get_table();
    for (int i=;i<=q;i++)
    {
        z=read();x=read();y=read();
        if (z) val[x]=y;
        else ask();
    }
    return ;
}