Codechef CHEFPRES—LCA

CHEFPRES

所谓一眼题，但是通过这道题学了c++的vector...

只想表示学语言什么的看别人代码最快了。。不想啃书

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std;
#define MAXN 100010
#define MAXK 110
vector<int> a[MAXK];
struct node{
   int y,next;
}edge[MAXN];
int f[MAXN][20];
int head[MAXN],deep[MAXN];
bool vis[MAXN];
int n,l,x,y,k,b,lfather,ans,ans1,st,q,p,sa;
void add(int x,int y)
{
    l++;
    edge[l].y=y;
    edge[l].next=head[x];
    head[x]=l;
}
void dfs(int x)
{
    vis[x]=1;
    for (int i=head[x];i>0;i=edge[i].next)
    {
        if (!vis[edge[i].y])
        {
            deep[edge[i].y]=deep[x]+1;
            f[edge[i].y][0]=x;//pre的一部分
            dfs(edge[i].y);
        }
    }
}
void pre()
{
    for (int j=1;j<=17;j++)
      for (int i=1;i<=n;i++)
        f[i][j]=f[f[i][j-1]][j-1];
}
int lca(int x,int y)
{
    if (x==y) return x;
    if (deep[x]>deep[y])
    {
        int t=x;x=y;y=t;
    }
    for (int i=17;i>=0;i--)
      if (deep[f[y][i]]>=deep[x])
        y=f[y][i];
    if (x==y) return x;//!!
    for (int i=17;i>=0;i--)
        if (f[x][i]!=f[y][i])
    {
        x=f[x][i];
        y=f[y][i];
    }
    return f[x][0];
}
int main()
{
    l=0;
    scanf("%d%d%d", &n, &k, &b);
    memset(head,0,sizeof(head));
    for (int i=1;i<=n-1;i++)
    {
        scanf("%d%d", &x, &y);
        add(x,y);
        add(y,x);
    }
    for (int i=1;i<=n;i++)
    {
        scanf("%d", &x);
        a[x].push_back(i);
    }
    for (int i=1;i<=k;i++)
        sort(a[i].begin(),a[i].end());//**
    memset(vis,0,sizeof(vis));
    deep[b]=1;
    dfs(b);
    pre();
    scanf("%d",&q);
    while (q--)
    {
        scanf("%d%d", &sa, &p);
        if (a[p].size()==0) printf("%d\n",-1); else
        {
        ans=0;
        for (int i=0;i<a[p].size();i++)//注意这里从0开始啦~
         {
             st=a[p][i];//像数组一样取数~
             lfather=lca(sa,st);
             if (deep[lfather]>ans)
             {
                 ans=deep[lfather];
                 ans1=st;
             }
         }
        printf("%d\n",ans1);
        }
    }
    return 0;
}