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  • CodeForces 385C 素数朴素筛法,穷尽数的素数因子

    //CodeForces 385C 素数朴素筛法,穷尽数的素数因子

     1 #include "iostream"
     2 #include "cstdio"
     3 #include "cstring"
     4 #include "algorithm"
     5 using namespace std;
     6 const int maxn = 10000100;
     7 int tot, pr[maxn];
     8 bool is_pr[maxn];
     9 int n, m, l, r, cnt[maxn], sum[maxn];
    10 
    11 int main()
    12 {
    13     int i, j, ans;
    14     scanf("%d", &n);
    15     for(i = 1; i<=n; ++i) {
    16         scanf("%d", &ans);
    17         ++cnt[ans];
    18     }
    19 
    20     memset(is_pr, 1, sizeof(is_pr));
    21     for(i = 2; i < maxn; ++i) {
    22         if(is_pr[i]) {
    23             if(cnt[i])
    24                 sum[i] += cnt[i];
    25             for(j = (i<<1); j < maxn; j += i) {
    26                 is_pr[j] = 0;
    27                 if(cnt[j]) {
    28                     sum[i] += cnt[j];
    29                 }
    30             }
    31         }
    32     }
    33     for(i = 2; i < maxn; ++i)
    34         sum[i] += sum[i-1];
    35 
    36     scanf("%d", &m);
    37     while(m--) {
    38         scanf("%d%d", &l, &r);
    39         l = min(l, maxn - 1);
    40         r = min(r, maxn - 1);
    41         printf("%d
    ", sum[r] - sum[l - 1]);
    42     }
    43 }
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  • 原文地址:https://www.cnblogs.com/AC-Phoenix/p/4288761.html
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