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     =          +       ;

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

 int main(){

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

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

     rep(i, , N - ) num[i] += num[i - ];

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

     return ;

 }