【第几小 / 分块】

题目

代码

#include <bits/stdc++.h>
using namespace std;

const int N = 1e5+10;

int a[N];
int br[N], bl[N], id[N], bcnt, L;
vector<int> bs[1010];

int main()
{
  int n;
  cin >> n;
  for(int i = 1; i <= n; i++)
    cin >> a[i];
  
  L = sqrt(n + 1);
  for(int i = 1; i <= n; i += L) //只保证了左边界不越界
  {
    bcnt++;
    bl[bcnt] = i;
    br[bcnt] = min(i + L - 1, n); //这是分块最容易错误的点，就是没有考虑右边界越界
    for(int j = bl[bcnt]; j <= br[bcnt]; j++)
      bs[bcnt].push_back(a[j]), id[j] = bcnt; //想直接用下标访问未初始化的向量，需要resize
  }

  for(int i = 1; i <= bcnt; i++)
    sort(bs[i].begin(), bs[i].end());
    
    int m;
    cin >> m;
    
  for(int i = 1; i <= m; i++)
  {
    int op;
    cin >> op;
    if(op == 1)
    {
      int x, y;
      cin >> x >> y;
      int t = a[x];
      a[x] = y;
      int bid = id[x];
      auto it = lower_bound(bs[bid].begin(), bs[bid].end(), t);
      *it = y;
      sort(bs[bid].begin(), bs[bid].end());
    }
    else if(op == 2)
    {
      int l, r, p;
      cin >> l >> r >> p;
      int cnt = 0;

      if(id[l] == id[r])
      {
        for(int j = l; j <= r; j++)
          if(a[j] < a[p]) cnt++;
      }
      else
      {
        for(int j = id[l] + 1; j < id[r]; j++)
        {
        	auto it = lower_bound(bs[j].begin(), bs[j].end(), a[p]);
        	if(it == bs[j].end()) cnt += br[j] - bl[j] + 1;
        	else cnt += (it - bs[j].begin());
        }
        for(int j = l; j <= br[id[l]]; j++)
          if(a[j] < a[p]) cnt++;
        for(int j = bl[id[r]]; j <= r; j++)
          if(a[j] < a[p]) cnt++;
      }
      cout << cnt + 1 << ' ';
    }
  }
}