hdu1754I Hate It(splay)

链接

线段树的水题，拿来学习一下splay.

本题涉及到求最大值以及单点更新，折腾了许久，差不多把splay搞明白了。

按位置建树，按位置是一颗排序二叉树，对于区间的操作非常方便，每次操作都将需要的结点转自根的右孩子的左孩子，因为加了2个结点，一个最小的，一个最大的，据说是为了防止越界。

这题只有单点，所以每次将所求结点旋自根节点即可。

 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<vector>
 #include<cmath>
 #include<queue>
 #include<set>
 using namespace std;
 #define N 200010
 #define LL __int64
 #define INF 0xfffffff
 #define key_value ch[ch[root][1]][0]
 const double eps = 1e-;
 const double pi = acos(-1.0);
 const double inf = ~0u>>;
 int pre[N],s[N],size[N];
 int ch[N][],a[N],val[N];
 int root,n,tot;
 void newnode(int &x,int k,int fa)
 {
     x = ++tot;
     ch[x][]=ch[x][] = ;
     pre[x] = fa;
     size[x] = ;
     s[x] = k;
     val[x] = k;
 }
 void pushup(int w)
 {
     size[w] = size[ch[w][]]+size[ch[w][]]+;
     s[w] = max(max(s[ch[w][]],s[ch[w][]]),val[w]);
    // cout<<s[w]<<" "<<w<<"// "<<" "<<ch[w][1]<<" "<<s[w]<<endl;
 }
 void rotate(int r,int kind)
 {
     int y = pre[r];
     ch[y][!kind] = ch[r][kind];
     pre[ch[r][kind]] = y;
     if(pre[y])
     {
         ch[pre[y]][ch[pre[y]][]==y] = r;
     }
     pre[r] = pre[y];
     ch[r][kind] = y;
     pre[y] = r;
     pushup(y);
     //pushup(r);
 }
 void splay(int r,int goal)
 {
     while(pre[r]!=goal)
     {
        if(pre[pre[r]]==goal)
         {
              rotate(r,ch[pre[r]][]==r);
         }
         else
         {
             int y = pre[r];
             int kind = (ch[pre[y]][]==y);
             if(ch[y][kind]==r)
             {
                 rotate(r,!kind);
                 rotate(r,kind);
             }
             else
             {
                 rotate(y,kind);
                 rotate(r,kind);
             }
         }
     }
     pushup(r);
     if(goal==) root = r;
 }
 int get_k(int k)
 {
     int r = root;
     while(size[ch[r][]]!=k)
     {
         if(size[ch[r][]]>k)
         r = ch[r][];
         else
         {
             k-=(size[ch[r][]]+);
             r = ch[r][];
         }
     }
     return r;
 }
 int query(int l,int r)
 {
     splay(get_k(l-),);
     splay(get_k(r+),root);
     return s[key_value];
 }
 /*void update(int l,int r,int k)
 {
     splay(get_k(l-1),0);
     splay(get_k(r+1),root);
     val[key_value] = k;
     s[key_value] = k;
     pushup(ch[root][1]);
     pushup(root);
 }*/
 void update(int l,int r,int k)
 {
     int kk = get_k(l);
     val[kk] = k;
     splay(kk,);
 }
 void build(int &w,int l,int r,int fa)
 {
     if(l>r) return ;
     int m = (l+r)>>;
     newnode(w,a[m],fa);
     build(ch[w][],l,m-,w);
     build(ch[w][],m+,r,w);
     pushup(w);
 }
 void init()
 {
     int i;
     for(i =  ;i < n ;i++)
     scanf("%d",&a[i]);
     ch[][] = ch[][] = pre[] = size[] = s[] = ;
     root = tot =;
     newnode(root,-,);
     newnode(ch[root][],-,root);
     size[root] = ;
     build(key_value,,n-,ch[root][]);
     pushup(ch[root][]);
     pushup(root);
 }
 int main()
 {
     int q,x,y,i;
     char sq[];
     while(scanf("%d%d",&n,&q)!=EOF)
     {
         init();
         while(q--)
         {
             scanf("%s%d%d",sq,&x,&y);
             if(sq[]=='U')
             {
                 update(x,x,y);
                 /*for(i = 0; i <= n+2; i++)
                 cout<<ch[i][0]<<" "<<ch[i][1]<<" "<<i<<endl;
                 puts("");*/
             }
             else
             {
                 printf("%d\n",query(x,y));
                 /*for(i = 0; i <= n+2; i++)
                 cout<<ch[i][0]<<" "<<ch[i][1]<<" "<<i<<endl;
                 puts("");*/
             }
         }
     }
     return ;
 }