BZOJ 3251 树上三角形

Posted 2020-08-21 ziliuziliu

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][20],dis[maxv],g[maxv],nume=0;
int s[maxv],top=0;
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=0;
    while (ch<‘0‘ || ch>‘9‘) ch=getchar();
    while (ch>=‘0‘ && ch<=‘9‘)
    {
        data=data*10+ch-‘0‘;
        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][0]=x;dis[v]=dis[x]+1;
            dfs(v,x);
        }
    }
}
void get_table()
{
    for (int e=1;e<=19;e++)
        for (int i=1;i<=n;i++)
            anc[i][e]=anc[anc[i][e-1]][e-1];
}
int lca(int x,int y)
{
    if (dis[x]<dis[y]) swap(x,y);
    for (int e=19;e>=0;e--)
    {
        if ((dis[anc[x][e]]>=dis[y]) && (anc[x][e]))
           x=anc[x][e];
    }
    if (x==y) return x;
    for (int e=19;e>=0;e--)
    {
        if (anc[x][e]!=anc[y][e])
        {
            x=anc[x][e];
            y=anc[y][e];
        }
    }
    return anc[x][0];
}
void get_push(int t)
{
    top=0;
    while (x!=t) {s[++top]=val[x];x=anc[x][0];}
    while (y!=t) {s[++top]=val[y];y=anc[y][0];}
    s[++top]=val[t];
}
void ask()
{
    int t=lca(x,y),tot=dis[x]+dis[y]-dis[t]-dis[anc[t][0]];
    if (tot>50) {printf("Y\n");return;}
    get_push(t);
    sort(s+1,s+top+1);
    int flag=1;
    for (int i=1;i<=top-2;i++)
    {
        if ((long long)s[i]+(long long)s[i+1]>(long long)s[i+2]) 
           flag=0; 
    }
    if (flag) printf("N\n");
    else printf("Y\n");
} 
int main()
{
    n=read();q=read();
    for (int i=1;i<=n;i++) val[i]=read();
    for (int i=1;i<=n-1;i++)
    {
          x=read();y=read();
          addedge(x,y);addedge(y,x);
    }
    dis[1]=1;dfs(1,0);get_table();
    for (int i=1;i<=q;i++)
    {
        z=read();x=read();y=read();
        if (z) val[x]=y;
        else ask();
    }
    return 0;
}