P2261 [CQOI2007]余数求和

P2261 [CQOI2007]余数求和

做法就是分块
k%i=k-(k/i)*i;
对(k/i)分块，一个细节问题就是n,k谁大谁小的问题

#include <iostream>
#include <cstdio>
#include <queue>
#include <algorithm>
#include <cmath>
#include <cstring>
#define inf 2147483647
#define N 1000010
#define p(a) putchar(a)
#define For(i,a,b) for(long long i=a;i<=b;++i)
//by war
//2019.8.21
using namespace std;
long long n,k,ans,l,r,t;
void in(long long &x){
    long long y=1;char c=getchar();x=0;
    while(c<'0'||c>'9'){if(c=='-')y=-1;c=getchar();}
    while(c<='9'&&c>='0'){ x=(x<<1)+(x<<3)+c-'0';c=getchar();}
    x*=y;
}
void o(long long x){
    if(x<0){p('-');x=-x;}
    if(x>9)o(x/10);
    p(x%10+'0');
}

long long sum(long long l,long long r){
    return (l+r)*(r-l+1)/2;
}

signed main(){
    in(n);in(k);
    ans=n*k;l=1;
    t=min(n,k);
    while(l<=t){
        r=min(t,k/(k/l));
        ans-=sum(l,r)*(k/l);
        l=r+1;
    }
    o(ans);
    return 0;
}