P3396 哈希冲突

题面

https://www.luogu.org/problem/P3396

题解

#include<cstdio>
#include<iostream>
#define ri register int
using namespace std;
int n,m;
int a[150050];
int ans[450][450];
char ch;
int main(){
  scanf("%d %d",&n,&m);
  for (ri i=1;i<=n;i++) {
    scanf("%d",&a[i]);
    for (ri j=1;j<=400;j++) ans[j][i%j]+=a[i];
  }
  int x,y;
  for (ri i=1;i<=m;i++) {
    ch=getchar();
    while (ch!='A' && ch!='C') ch=getchar();
    scanf("%d %d",&x,&y);
    if (ch=='A') {
      if (x>400) {
        int sum=0;
        y%=x;
        for (ri j=y;j<=n;j+=x) sum+=a[j];
        printf("%d\n",sum);
      }
      else {
        printf("%d\n",ans[x][y]);
      }
    }
    else {
      for (ri j=1;j<=400;j++) ans[j][x%j]-=a[x];
      a[x]=y;
      for (ri j=1;j<=400;j++) ans[j][x%j]+=a[x];
    }
  }
}