luogu P2617 Dynamic Rankings(分块，n <= 1e4)

嘟嘟嘟

带修改区间第k大。

然而某谷把数据扩大到了1e5，所以用分块现在只能得50分。

分块怎么做呢？很暴力的。

基本思想还是块内有序，块外暴力统计。

对于修改，直接重排修改的数所在块，时间复杂度O(√nlogn√n)。

对于询问，二分答案，然后在每个块内再二分统计小于mid的数有几个，块外暴力统计，时间复杂度O(m * log1e9 * √nlog√n)，所以只能过1e4。

 #include<cstdio>
 #include<iostream>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #include<cstdlib>
 #include<cctype>
 #include<vector>
 #include<stack>
 #include<queue>
 using namespace std;
 #define enter puts("")
 #define space putchar(' ')
 #define Mem(a, x) memset(a, x, sizeof(a))
 #define rg register
 typedef long long ll;
 typedef double db;
 const int INF = 0x3f3f3f3f;
 const db eps = 1e-;
 const int maxn = 1e5 + ;
 const int maxb = ;
 inline ll read()
 {
   ll ans = ;
   char ch = getchar(), last = ' ';
   while(!isdigit(ch)) {last = ch; ch = getchar();}
   while(isdigit(ch)) {ans = (ans << ) + (ans << ) + ch - ''; ch = getchar();}
   if(last == '-') ans = -ans;
   return ans;
 }
 inline void write(ll x)
 {
   if(x < ) x = -x, putchar('-');
   if(x >= ) write(x / );
   putchar(x %  + '');
 }

 int n, q, a[maxn];
 char c[];

 int S, Cnt = , blo[maxn], lb[maxn], rb[maxn];
 int b[maxb][maxb];
 void init()
 {
   S = sqrt(n);
   Cnt = n % S ? n / S + : n / S;
   for(rg int i = ; i <= Cnt; ++i) lb[i] = rb[i - ] + , rb[i] = lb[i] + S - ;
   rb[Cnt] = n;
   for(rg int i = , j = ; i <= n; ++i) blo[i] = j, j += (i == rb[j]);
   for(rg int i = , cb = ; i <= Cnt; ++i, cb = )
     {
       for(rg int j = lb[i]; j <= rb[i]; ++j) b[i][++cb] = a[j];
       sort(b[i] + , b[i] + cb + );
     }
 }
 inline void update(const int& x, const int& k)
 {
   a[x] = k;
   int t = blo[x], cb = ;
   for(rg int i = lb[t]; i <= rb[t]; ++i) b[t][++cb] = a[i];
   sort(b[t] + , b[t] + cb + );
 }
 inline int judge(const int& L, const int& R, const int& x, const int& k)
 {
   int l = blo[L], r = blo[R], ret = ;
   if(l == r)
     {
       for(rg int i = L; i <= R; ++i) ret += (a[i] < x);
       return ret < k;
     }
   for(rg int i = l + ; i < r; ++i)
     {
       int tp = lower_bound(b[i] + , b[i] + rb[i] - lb[i] + , x) - b[i] - ;
       if(tp < ) tp = ;
       if(tp > rb[i] - lb[i]) tp = rb[i] - lb[i] + ;
       ret += tp;
     }
   for(rg int i = L; i <= rb[l]; ++i) ret += (a[i] < x);
   for(rg int i = lb[r]; i <= R; ++i) ret += (a[i] < x);
   return ret < k;
 }

 int main()
 {
   n = read(), q = read();
   for(rg int i = ; i <= n; ++i) a[i] = read();
   init();
   for(rg int i = ; i <= q; ++i)
     {
       scanf("%s", c);
       if(c[] == 'C')
     {
       int x = read(), y = read();
       update(x, y);
     }
       else
     {
       int L = read(), R = read(), k = read();
       int l = , r = 1e9;
       while(l < r)
         {
           int mid = (l + r + ) >> ;
           if(judge(L, R, mid, k)) l = mid;
           else r = mid - ;
         }
       write(l), enter;
     }
     }
   return ;
 }