Codeforces 546D Soldier and Number Game(数论)

类似筛素数的方法……求出前缀和。然后直接O(1)回答即可。

#include <bits/stdc++.h>

using namespace std;

#define rep(i,a,b)              for(int i(a); i <= (b); ++i)

const int N     =    10000000      +       10;

int num[N];
bool p[N];
int T, n, m;

int main(){

    memset(p, true, sizeof p);
    memset(num, 0, sizeof num);

    p[1] = false;
    rep(i, 2, N - 6) if (p[i]){
        for (int j = i; j <= N; j += i){
            int tmp = j;
            while (tmp % i == 0){
                ++num[j];
                tmp /= i;
            }
            p[j] = false;
        }
    }
    
    rep(i, 2, N - 6) num[i] += num[i - 1];

    scanf("%d", &T);
    while (T--){
        scanf("%d%d", &n, &m);
        printf("%d
", num[n] - num[m]);
    }

    return 0;

}